Nope. I had a pro on my old 32" 720p tv before I bought a 4k set earlier this year. You will still get better performance and I think it will do supersampling on all games even if they don't have pro features built in.
I wouldn't unless you're interested in the PS exclusives like GoW, HZD, Spider-man, Tsushima et al and think you'd actually buy them. Also, you'll have a 4k TV sooner or later if you plan on buying one anytime soon as it's not like you can find a decent TV that isn't 4k at this point. Just be honest with yourself and tally up what you'd think you'd spend on the whole experience (console AND games), and figure out whether or not it's worth it. If you want to play the games, but aren't in a rush to do so, waiting until next gen and buying all used is another option.
For sure. You could easily buy a copy for the PS4 by the time you got one, or trade in your xbox copy towards it. Or hell, maybe PS5 will have full backwards compatibility and you could play it on one of those. Consider in your choice that you're currently worrying about wasting a couple dozen bucks to the point of considering purchasing something for several hundred, which is usually a sign of bad decision making, or that you've been wanting one bad enough that it's leaking into your choices without realizing it.
If $400 isnt' a big deal I'd spend it on the Pro and get RDR2 on that. I posted somewhere in the RDR thread but basically RDR 2 will run full 1080p on the PS4 Pro, but run at UNDER 900p on the stock xbox one/S. I think thats a massive difference. It will run the best on the X but it doesn't really make any sense to go from xbox to X unless there is a crazy good trade deal. And if you are only going to be playing 1 game for the next 3-4 months, and if money isn't that huge a deal, may as well play it in the best way you can, right? Then you'll also have a nifty backup set of games to play if you get a little bored or want some variety, whereas there really isn't much on the Xbox that I'd say is a MUST PLAY other than FH3/FH4/Halo MCC. PS5 is probably at least 18 months out, they are just now talking to devs about what it may be so specs aren't even close to finalized and its always 1 year to go from final design to just factories running at full steam.
The best deal of course will be around BF but right now you can buy the PS4 Pro with RDR 2 bundled for $399 total, there will probably be a decent deal when its released on 10/26 (same day as RDR 2) and you are saving that $60 you'd spend on the game.
If anyone is interested in checking out PS Now since they added the downloading, the free trial has apparently reset for those that had used it before. I tried RDR (not available for downloading) and it felt like complete ass. Unsure if that's the service or the game itself though.
Bloodborne, TLOU, Spider-Man, God of War, Yakuza 0 (also on PC tho), Uncharted 1-4, Until Dawn, Horizon Zero Dawn, and Persona 5 make it a no brainer for $275+ plus Kingdom Hearts III, Days Gone, Ghosts of Tsushima, Death Stranding (lulz), and TLOU 2 in 2019 with probably more announcements at E3.