I want to build a PC which can run all AAA titles at 4K and also for streaming. My budget is $5000. [Intel 8th Gen.At least 32 GB RAM.GTX 1080 ti (SLI if possible)]
For both? I'd get at least X299 or a 1920X at minimum on that kind of budget. Yes it's overkill but for those purposes I wouldn't get anything less. If you're going to multitask you want a PC that can keep up with it, and this is where having more cores comes at an advantage. This is what I would suggest:
Can I put it two extra 16 GB sticks and make the memory 64 GB coz I need it for streaming and video editing as well coz I am a photographer
Yeah for that you will have to make sure you get a matching set. No matter how much RAM you get it *ALWAYS* has to be a matching set. I know it will be more expensive that way but on your budget you shouldn't have to worry about that.
After some years down the line. Is 8700K more reliable or Threadripper 1950X ?
Threadripper isn't really a gaming CPU. It has that purpose but when you run it in game mode it can actually slow down overall gaming performance. If you want to go higher end, then I would suggest a higher end Intel CPU and go LGA 2066, and get something like a i7-7820X or an i9-7900X, but even then the higher end CPUs still aren't really meant for gaming purposes.Yes you can game on them but games aren't really optimized to run on these CPUs, at least not yet.