Sjaakie

If it works well there is probably nothing to worry about just let it do its thing. If youre worried about crypto mallware do a fresh windows install for peace of mind.

NH-D15 is great for gaming on any cpu. What is the problem with your 5800x? Have not seen any problems yet for the 7800x3d it is highly recommended for gaming for its insane price / performance. AMD gpu's have better raw performance indeed but in general Nvidia will have less issues and the better tech in terms of DLSS / ray-tracing. I wouldn't get the RM850e if you go for silence, better get the RM850x or maybe a Seasonic GX-850 3.0.

6400 is very ambitious, most likely the cpu mem controller cant handle that. Just turn it a bit lower and see if that revolves it. Try 6000. AMD only guarantees up to 5200 on that chip, above that you need to be lucky. Though 5600 / 6000 is usually fine.

Did you already install the 5800x3d? Could be that the new bios dropped support for the 1400.

For Adobe and video editing in general it is highly recommended to go Nvidia for Cuda suppport.

No it's not much worse on the 7900 / 7950x3d, just not worth it for just gaming as they're more expensive and perform a bit less. Check the benchmarks online. If you can use the cores for productivity work like photo editing they may be worth it. I'd rather get an EXPO kit, they're optimised for Ryzen. XMP is for Intel.

Looks good. 64 GB is a bit overkill but could be good to get now its still pretty cheap. Is it an AMD EXPO kit, and not an Intel XMP kit? 6400 MHz is very high you may not reach that speed. Though you can run it lower if it doesn't run stable. Your psu does not seem to come with 12vhpwr connector. Rather get a https://de.pcpartpicker.com/product/RqYmP6/seasonic-vertex-gx-1000-1000-w-80-gold-certified-fully-modular-atx-power-supply-vertex-gx-1000 which has a native connector and is ATX3.0 / pcie5.0 specced. For gaming the 7800x3d is the better choice, 7900 and 7950x3d are a bit worse due to the cache layout. Unless you can really use the extra cores for photo-editing.

Poco F5 is pretty solid price / performance wise if you can tolerate the bloatware. Samsung A54 is decent. Motorola has some very decent price / quality options. I you go used I'd look for a Galaxy S21 / S22. Many people upgrade their flagship after 1 or 2 years and sell their old one for a good price.

Sure, depending on the game and your settings / expectations ofcourse. Many AAA will run at a lower framerate. Are you looking at 1080p?

Are you happy with the performance for current games? If you are don't upgrade now, upgrade when you need it. You'll get faster hardware for your money in the future. GTA 6 for pc will take at least 2 more years.

Not the best but certainly not the worst. It could be higher but it depends on the cooling / chassis / luck with the chip. Maybe some bloatware in the background taking up resources.

Were they part of a raid pool? How old is your previous system? Maybe look whether they boot with CSM / legacy boot enabled in bios. Most straight forward fix would be to install a fresh windows install though you would lose all data and start fresh.

Get an external 20 / 40 Gbs NVMe enclosure, slap in a fast SSD and you'll have a really fast and relatively small external ssd.

The internet works at lightning speed

Do they work fine seperately? Kits are tested to work together though I would expect 2 sticks with equal part number to be ok especially running them at a lower speed. Maybe just got unlucky. If they work fine seperately maybe just bump down the speed to 3000 and call it a day if that makes them work together.