Bashrag

Good to know! Thanks! 
I know - just by looking at the two it seems the Octo can take 8 fans as against the 4 fans that the quadro can take. But I don't know if there are any other differences. More importantly, I don't know if I can daisy chain 3 ML 120s on my top rad and plug them into fan header 1 and then daisy chain the 3 fans on my bottom rad and plug them into fan header 2 - if this is possible, the Quadro should be enough. If I need to plug 6 fans into 6 separate headers though, then I'll need an Octo, obviously.
This is what I was looking for - thank you!
Can those fans be controlled? Can you set a custom curve for those fans? I haven't seen any chipset waterblocks so I'm not sure if that's an options.
I read up a bit and it seems that the Octo ships with a temp sensor so I assume it can control fans based on coolant temps. I didn't know that bit about the flow meters. Thanks!
Understood. I'm still on the fence about putting the 2070 S under water - the general opinion seems to be that it doesn't make much sense from a performance perspective and that I shouldn't bother with a water block unless I have a 2080 S, 2080 Ti or a higher-end 30XX card. 

for your consideration: https://www.ekwb.com/shop/ek-quantum-momentum-chipset-aorus-x570
I'm not so well versed with x570 boards so you'll have to check your own.

The additional VRM cooling offered by the monoblock is unneccesary and should be perceived as an aesthetic piece, it also taxes your cooling loop quite substantially as the VRMs do get quite hot (but they can take it). The bigger problem in my opinion is the chipset fan for X570 which can be a source of annoying noise once the rest of the system is quiet. Brass is fine for fittings, almost all angled fittings are brass, radiators also typically use brass on their ends.  
 
Personally I do believe that watercooling loop fans need/should be controlled by the fluid temperature to ensure quiet and efficient operation, and so therefore a 2-pin temperature sensor that plgus into the OCTO would be desirable (I assume it can control fan speed by a temp input, otherwise the device is stupid). Flow meters are less necessary in my opinion since you can plug the pump into the CPU_FAN header which will cause a shut down if the pump were to not report an RPM.
 
CPU blocks are quite wide compatible so I wouldn't worry about it, if you do intend to upgrade the GPU, definitely do that before buying a block. Having said that GPU's are watercooled much more effectively than CPUs so I find watercooling GPUs for silence to be a good use.

Re:b
copper and brass shouldn’t interact I think.  Brass has copper in it.  Bronze is copper and tin.  Brass is copper and something else (I forget what)  brass content can vary a lot.  Some chineses brasses have large amounts of lead (eek!) in them which might cause issues.  I don’t know.  Copper and many (but not all apparently) kinds of steel can react (there are apparently several kinds of stainless and some other alloys that don’t) and copper and aluminum can react. Nickel is usually nickel plated brass so that may be considered brass as well.
 
re: c
quadro means “four” octo means “eight”.  I dunno if that’s helpful or not.  I’m not seeing references to either term so I don’t know what additional ramifications might apply in this instance.

Just an FYI, the last time I looked at this (it was well over a year ago, probably closer to at least two years) it was actually cheaper to buy on Amazon UK (with ifixit as the seller) even with the (10%? I think) discount code they had going at the time as it had free postage. The ifixit EU store had paid postage and the conversion was slightly better to GBP. Although you will use the Euro where you are, that might not be the case for you, it might be worth looking up the cost on whatever the nearest Amazon store is to you, if they have it on there and you are going to actually buy it.

Thermal pads are not really designed for CPU usage even if they're marketed towards it. Thermal Paste is almost always going to be superior in performance vs a thermal pad. 
 
 

No, never use thermal pads for a CPU or GPU.
 
MX4 lasts over 8 years you don't need to buy a new tube.

@AkshayRao27
Can I just say... That's the best formatted forum post I've seen. Well done, I hope you find some AWESOME wireless headphones and enjoy them.

Thanks so much for all of your feedback. I updated the parts list based on what y'all have been saying. I'm out right now so I can't have a look at all of the PSU calculations, but once I'm home, I'll have a look at all of the number crunching y'all gave done and make updates / answer questions.
 
So far, y'all have ended up saving my SO €100 and optimised stuff quite a bit as I see it ^^

Those calculations are wrong. 
 
Firstly, your calculations are based on the PSU outputting 650w at all times. The PSU only outputs as much power as the system draws. When you're idling or just browsing the web, watching a video on YouTube, etc you'll be closer to 50-100w consumption. 
 
For a system with a 3700x + 2070 super you should be under 400w peak power consumption under load. Probably closer to 300-350w. While browsing the web or just left open on desktop like 75w or less.
For arguments sake let's say 100w power consumption under general use (web browsing, etc).
A gold rated PSU will be pulling 113w from the wall
A titanium rated PSU will be pulling 106w from the wall.
Difference of 7w. Over 8 hours of use a day that's 0.056kwh, or 0.392kwh per week. That's a difference of 20kwh per year, and at the €0.10/kWh in your table that's €2 per year.
 
Let's say you're using your system intensively and those 8 hours of use per day are not at 100w, but instead under a heavy load with the system pulling up to 400w. 
Gold rated PSU will be pulling 435w from the wall.
Titanium rated PSU will be pulling 415w from the wall.
Difference of 20w. Over 8 hours of heavy use that's a difference of 0.16kwh, or 1.12kwh per week. Difference of 58kwh per year, which at a €0.10/kWh will be €5.80 per year you would save with a titanium unit.
 
So it depends on how much you'll use the system and what sort of load it will be under, but for most people with typical usage you'd only be saving a few euro per year at most.
 
(Power consumption and efficiency calculations are a little guesstimated and based off the 80+ standards efficiency targets not actual PSU efficiency graphs... I'm on my phone. Should be close enough to give you an idea though)
 
The prime titanium is a good unit, but you could probably get a decent 80+ gold unit for under €100. 80+ titanium might save you €5 a year but it's an extra €80 euro upfront. Probably won't pay for itself over the lifetime of the unit. At €5 savings per year from efficiency it would take you over 15 years to make the cost back.

None of the above. The 2070 Super is a 215W card, so expect the whole system to draw a bit under 300W when gaming. Using actual efficiency numbers for the BitFenix Formula 450W (€65 on PCPP DE) and Seasonic Prime Titanium 650W (€175) on 230V AC at about 300W, they are about 91,5% and 95,2% efficient. If you drink so many energy drinks that you don't need any sleep, and you game 24/7, you save about €38 €11 annually with the electricity cost you used. Of course, if you e.g. game "only" 8 hours per day, every day, that's under €13 €4 annually. You get the idea. 
Efficiency numbers from Cybenetics, on 230V. 
https://www.cybenetics.com/index.php?option=power-supplies
The Formula 450W is the my recommendation for a cheap, fairly high end, quiet PSU. Not modular, but that should be fine. 
 
The 2070 Super performs about 20% better than the 2070. €57 is 4% of the total price for a €1500 PC. 4% price increase for 20% better performance should be worth it. 
As for the 5700 XT, the reference cooler is crap. AiB cards will be out in mid-late August. The performance is about 8% worse in games. 
 
Other than that, you can easily save money by going for a less expensive motherboard. Check out the MSI B450-A for €87. It might require a BIOS update, but that can be done without a CPU on that board. 
If you want a nicer SSD, check out the Samsung PM981 for €82 on PCPP DE. 
When checking case reviews, check the date of the review. Standards change, so a case that's 8 years old might not be as good as a more modern case, even though the reviews are more positive. 
Combining important work with overclocking might not be the best idea. System stability might be more important than the little performance gained. Especially with Ryzen 3000, which barely benefits at all. 

Thank you so much, folks. 
To everyone asking me why I didn't consider getting something new with that budget: I had absolutely no idea I could get something of this level at that price point. I've only ever used gaming laptops and they tend to be a fair bit more expensive. I will definitely look into these builds in detail when I'm off work. Totally going to play around with PCPartPicker later today and see what all I can put together! I'll also check local stores to see how the prices match up