I just installed my x99 motherboard and 5820k. I power it up and I go into the bios where I can use my keyboard and mouse but as soon as I boot into Windows I am unable to use them.
It's a gamble with cards that were used for mining. Buying used cards though is fine. I bought a 660 used from hardware swap for $50 and it works fine.
I honestly think you would like either one you get and would not regret it. That being said, my personal choice would be 21:9 because I have never owned a 21:9 monitor and I would rather have an ips panel than to 144hz.
I painted my mobo heatsinks on my z97 system with paint from hobby lobby that is used for model cars. The only "negative" effect is that it voids the warrenty so if you want to avoid that use plastidip. With plastidip you can just peel it off incase you need to rma it.