1. You don't need 750w psu for a single gpu build even if you OC unless you'll go dual gpu which is the case that you need to go with a 750w. You can go with a 500w psu if you'll run on single card, but better get 550w/600w If you're that cautious. And I will also suggest that you get a 550w instead which will save you some money.
2. Yes, most will suggest getting 8gb ram instead even I would suggest that. But since you're pretty decided getting the 16gb, it's still fine.
3. Everything else is quite good and yes will run on ultra at 1920x1080, just don't forget a cooler once you plan to OC that CPU. a hyper 212 evo will do.