In your case I believe an Intel processor would be ideal due to speed. AMD processors tend to be more useful for virtualization, which you don't seem to have a need for.
DDR4 would be your best bet since it's much faster than DDR3.
I wouldn't focus on the brands too much between NVIDIA and AMD, what you'll want to focus on more is the chip-set, GTX or R9. From what I understand though if you plan to get a GPU with 4GB memory the R9 makes better use of it.
***Note: might want to make sure the GPU uses DDR4.
If you use pcpartpicker
to create a parts list it will give you an estimate of the wattage you will need. With that estimate of wattage I suggest finding a power supply with at least 2 times that, with a gold or platinum rating.
In regards to:
It's slow and filled with bloatware and crapware and has some malware and a trojan horse.
You could use such things as CCleaner and Malwarebytes to help keep your pc clean.
Basically it comes down to what your budget is for this build. Also what OS you plan on using?
I hope this answers your questions.