256GB Is a lot for Nintendo games, which is why 90% of people will be buying a Switch 2.
Most first party Switch 2 games will probably be 20-30GB outside of future Zelda's & RPGs. Ratchet on PS5 is 40GB.
500GB would be great if Nintendo wanted to encourage 3rd party sales/downloads out the gate as they will most likely average 70GB for AAA ports but if the expandable memory is relatively cheap, it doesn't really matter. This is infinitely better than the 32GB which could barely hold Zelda BOTW
256 GB will hold whatever new Mario game is announce, Smash, a bunch of smaller titles, the new COD and a free to play game like Fortnight. That's a good starting point IMO but of course 500GB would be the sweet spot.