Ramaddil

So by checking this, it looks like the issue is not CPU getting maxed, nor a network bottleneck.
 
You might want to try a fresh install of Plex at this point - uninstall, manually delete any remaining Plex folders, reboot, reinstall, try again.
You shouldn't be DMZ'ing the system at all. DMZ (at least, assuming it's a "proper" DMZ and not the fake bs a lot of consumer routers rock) puts the entire system on the outside of the firewall.
 
All you need to do is assign a static IP to the system, and port forward - no DMZ required, period. In fact, it's an added security risk so I highly recommend you change that particular setup.

A VPN would work, assuming you could get the server working. 
 
You would setup a VPN server on your network, then connect to it remotely. There are a few different vpn protocols you could use, including L2TP and OpenVPN. 
 
Once connected, the app should find your plex server as if you were locally connected. 

My System is updated as well whenever you get time to update it. 
 
 

How do you know its a mobo issue? Use a UPS or line conditioner for the power

If you're not willing or able to run a longer ethernet cable through or around walls (and I completely understand that) and you don't want Wi-Fi, you could try a powerline adapter. Just be aware that the connection may see some degradation, particularly in older wiring. Also, if you have multiple breakers, the signal will not reach circuits on both.

Instead of a radiator and a pump, why not just get a passive air cooler? The Tisis Core edition comes without a fan, but it should be enough to cool a low power CPU. 
Other than that, do keep in mind that hard drives will produce noise, so go for all SSD, if that's a priority.
Instead of a dual core CPU, consider one of the lower power Ryzen chips. 

1030 is a waste of money

I wouldn't use a laptop unless it is modern.. Old Laptops have slow processors and they are not built for transcoding.  Your FX6300 would be better.  You dont need a Graphics Card like that for a server.  It uses alot of power, get a low power card just to be able to have a GUI.  I used a Zotac GT710 1x pcie for all my server machines just to have video.  Internet speed is great.   
 
FX6300 has a passmark score around 6300 at stock speeds.  That should be able to handle at least 3 1080 transcoding  streams and possibly some direct streams.  If you need more streams you could invest in a 8000 series fx chip on the cheap from ebay.
 
I run Windows 10 with Plex, file storage and other programs.   

Theoretically, Intel will release an 8-Core Coffee Lake or Cannon Lake CPU as an 8th Generation i9 in Q3, hence why there is no 2800/2800X, which is rumored to be reworked to be a 10-Core to dominate the workstation scene.
 
The 2700X is the better choice of the two, with more cores and threads, as for if you should wait, it depends on how urgently you need it.

Please keep in mind that redundancy and backups serve different purposes.
 
Redundancy exists to save you time and effort. If a physical failure happens, you pop in the replacement, and in a (mostly) automated fashion, the array rebuilds itself.
 
Whereas a backup will protect you in case of actual data loss due to accidental deletion, malware infection, corrupted files, etc.

First we need to know what OS you are running, second are all three drives the same size? You can do Storage Spaces in windows for a NAS, or if you do freenas you can do a HBA like some of the posters have suggested.  You can do a raid card if that is something you want to do.. I have been using raid cards in my Windows PC for years and all these people saying you cant use without a back-plane are wrong.  On top of that I have had little to no problems with my setup.. I have a Raid 6 with 28 drives, a Raid 5 with 3 drives and another raid 5 with 10 drives.  All used in different manners one is a backup array.  Most of the used raid cards on eBay are decent they last for awhile but run hot so you need to make sure you have enough fans to cool them down.
 
It depends on what you intend to run on your NAS which will depend on what hardware or software you want to use.  They have software raid options on the market as well.

If you want longer run time most UPS support battery expansion modules, which have larger battery units in them than the UPS.

if it works in other slots then its the motherboards slots

im personally not a big fan of buying old Server hardware because you will often run into problems and will need to search for one with many SATA ports in this case.
 
also for me power consumption is extremely important because electricity is expensive here, having a device that just uses 50 watts more means it will cost me about 130€ a year extra to operate so i rather invest in more efficient hardware and save the money in the long run.

PCPartPicker part list / Price breakdown by merchant
CPU: AMD - Ryzen 7 2700X 3.7GHz 8-Core Processor  ($319.99 @ Amazon) 
CPU Cooler: NZXT - Kraken X62 Rev 2 98.2 CFM Liquid CPU Cooler  ($146.49 @ SuperBiiz) 
Motherboard: MSI - X470 GAMING PLUS ATX AM4 Motherboard  ($129.14 @ Amazon) 
Memory: G.Skill - Ripjaws V Series 16GB (2 x 8GB) DDR4-3200 Memory  ($164.99 @ Newegg Business) 
Video Card: Asus - GeForce GTX 1080 8GB ROG STRIX Video Card  ($579.00 @ B&H) 
Power Supply: EVGA - SuperNOVA NEX 650W 80+ Gold Certified Fully-Modular ATX Power Supply  ($55.98 @ Newegg) 
Total: $1395.59
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-05-22 21:11 EDT-0400

This is true NAS hard drives are not needed but are similar in price and come with longer warranty periods and are better for vibration and long term use.  I have Red drives that have been going for 5 plus years with no issues at all.  Buying sub par drives can lead to data loss or early replacement.
 
Yes you can add more sata slots, look for Pcie sata expansion cards.  
 
Raid 1 is the same as copying data the same data to two drives.  It is easier to put the drives in raid 1 in windows instead of on the motherboard. Especially if you transfer the drives to a new motherboard/system it will be able to recognize them without having to reinitialize. 

Protecting any data that you can not loose should have 3 copies of it.  In your situation if these photos are that precious to you then you should do the following.  Create or Buy a NAS, if you are not tech inclined then buy a Drobo/Synology or similar product fill it with drives and create a backup strategy to have two copies of your data.  Then have a off site backup of your data via cloud storage or physical drives stored off site.  This doesnt have to be done all at the same time but the soon you do it the safer your data is.
 
I currently employ this strategy I actually have 4 copies of my data.  Off Site Physical Storage, 1 Primary Server, 1 Backup Server and external drives that are portable.  Raid is not a backup... If you want to explore building a nas then you can use freenas or a similar product.  There are plenty of examples of how to build and run a nas on these forums and everywhere on the net.
 
Do your research.. External drives are not a good idea unless you are using them for off site storage.  Most of them die prematurely unless they are in a quality enclosure with proper airflow.  Invest in good drives that are reliable WD Red and Seagate Ironwolf drives are nice.

Reviews on that MB kinda stink.. Go with this
 
 https://www.newegg.com/Product/Product.aspx?Item=N82E16813144019&cm_re=b350-_-13-144-019-_-Product
 
has a 15.00 rebate to make it 59.99 after rebate.

As someone who's worked as a journalist, I tend to take the side of other journalists and analysts over entertainers with faulty methodology, but at least we can agree to disagree, when what is important here is that the 8400, at it's present price at least, is not as good a buy as a Ryzen CPU and mobo combo (1600 or above).

The i5 8400 comes with a stock HSF, which is enough to run it at stock clocks.
 
Agreed that the 2600 would be the better option than a 1600X. The 1600 does come with a stock HSF though, and is probably the best value IMO, especially when it goes on sale, retailers have to clear out the old 1st gen Ryzen stock now that Ryzen 2000 series is here.

If you had a budget for a 8700 or 8600 then for sure it would be a better buy over ryzen for gaming but the 8400 is not a good buy at that price point when there is r5 1600 or 2600x there.  my 2cents

I would include a 1600 in that too and it will still perform better for video editing and streaming than the 8400.

I agree with this but if you have to have it now I think the b350 + 1600 is a good deal.

The 2600X alone is $230, good luck finding a motherboard for $20
 
To the OP, either a Ryzen 1600 + cheap B350 motherboard for an all round machine
 
OR i5 8400 + B360 motherboard for a gaming machine
 
Avoid the A350 and H310 mobos if you can

67C is not hot at all