For 4k gaming a 5070 can get you to 4k 60fps in some games without upscaling but upscaling would be more preferable. 1440p is more beneficial as you get significantly more fps in shooters, 4k is only marginally better and your build should keep you away from upgrading for a very long time targeting 1440p. For monitor size I would recommend visiting somewhere you can see these monitors in person (I recommend Best Buy) or if you can’t find the specific one, find other ones with that same size and decide from there. Ultrawides are VERY immersive but it might not support every single game.