Will the 64GB be big enough? 
Discussion
Yeah I recommend buying a 256 GB SD card on Amazon and that'll be perfect for it
Starfield is 114 GB so you'll want the 64 GB and an SD card, but you can also just get gamepass for like 5 bucks and play it over Xbox cloud gaming if you're trying to do budget mode 🤝 https://www.rockpapershotgun.com/how-to-play-starfield-game-pass-on-steam-deck