The answer to all your questions is preference. You have to use the different types/combinations in order to find out what you prefer to use the most.
Curved monitors are alright, I've used it and I honestly think curved is the way to go for big ultrawides, and by that I mean if your monitor is really close to you, you would benefit from a curved monitor. After just a short while you won't notice it's there and I really liked that. I'm personally going to buy the LG UM68-P,
https://www.amazon.com/LG-29UM68-P-29-Inch-21-UltraWide/dp/B01B9IDLAW/ref=sr_1_1?ie=UTF8&qid=1472245938&sr=8-1&keywords=lg+um68-p
$299.00
Flat
29"
21:9
2560*1080
75 Hz
IPS
FreeSync (48 Hz to 75 Hz)
I use an AMD XFX R9 380, and for me that's a great match I think. G-Sync monitors are overpriced for the most part, yes they do have more hardware for the ULMB feature, but I still can't justify jumping to NVIDIA to enjoy the same exact thing, not counting ULMB which to me is not needed.
All the best!