Well, you certainly haven't overpaid...whether it's the best system for your uses and your monitor (assuming it's being used for gaming...ignore if not) is a different matter. Regarding the RAM, while AMD chips do love higher frequencies, for a normal system 3000 will be fine....my system is not far different to yours and it runs fine on 3000.
Hmmm...well, for gaming purposes on a 1080p monitor you will be fine.....but streaming at the same time will push the 3600 (generally the 3700 is the minimum chip for gaming/streaming), although you might get away with it for FIFA and FM. Video editing I definitely would have again been looking at the 3700 as the extra cores come in handy...again, the 3600 can do it, it just may push the chip quite hard.
What I would say is keep on eye on CPU temperatures and load while editing or gaming/streaming and if either or both are consistently high, I'd look at getting an aftermarket CPU cooler.....the stock AMD cooler is excellent but it has it's limits and anything to prolong the life of the chip is a good thing.