Need a new computer, but very confused!

I built my last computer, about 8 years ago. It's now slow and doesn't run Premiere Pro CC very well - Lumetri effects cause PP CC to crash on rendering. The GPU is ancient, with 1GB RAM. It has 24GB of system RAM and lots of  spinning hard drives. The C: drive is an SSD.

Time to get a new machine, but the more I read, the more confused I'm getting! Surely it should not be so hard to get a system that'll give me real time previews in PP CC of 4K H.264 video, with some effects applied, and give me decent fresher times? I do just a little in AE, but not much, so rendering times in AE are not a priority for me.

I'm looking at getting a good video card, probably the GTX 1080TI. I'll use this computer for flight simulation also.

Assume I have a good storage setup, with a 1TB SSD for the system and program drive, and other drives for media and cache files.

I'll have 64GB of RAM.

What processor should I be looking at?

What type of motherboard?

I'm not sure I want to build my own system again, but if I can give a builder my specs, or buy a complete system from a reputable supplier, that would be preferable.

Can anyone help me out? Please tell me why you recommend what you do, and keep it as simple as possible! I'm not a tech newbie, but I haven't followed the CPU trends for a few years and have been left behind.

As an aside, it seems to me that Editing Systems seem to be quite a bit more expensive than Gaming Systems with similar hardware specs (ignore all the drives that Editing Systems generally come with). In fact, Gaming Systems frequently use faster RAM, and may even be overclocked and water cooled. Why not go for a gaming system? Is the higher price of the Editing System just because it's for "professional" use?

Thanks for your help.