I guess it depends on how you ride but I spent a week with them last year and I only remember one puncture. I used High rollers with single ply DH casings (and was glad I did) but others had 2.1 Panaracer Fire XC (crazy in my opinion), Nobby Nics, etc. There weren’t any thorny trails but pinch flats are a real possibility, so as long as you have good sidewalls and a reasonably high volume you should be fine.
Brakes wise – you can pull a 203 rotor more gently but it is very hard to pull a 180 harder! Go for the bigger option you can. Probably the cheapest option to improve your “alpine experience”.
And as other have said, shorter stem, wider bars if you want to but importantly make sure you are happy on the bike and used to riding it on demanding terrain with your tyres of choice before you go.
Personally from your bikes I’d take the ST4 but you will have more fun on the bike you feel happiest and most comfortable on.
Have fun!
P