Well Switch has no games so logically...
Anyway. You have a chance to possibly avoid pirate syndrome/the paralysis of choice. Keep it small and the collection you walk about with lean and you might enjoy things more than having near everything rammed onto a 512 gig setup and then not wanting to play anything.
Generally though figure out the sizes of the sorts of games you like and multiply accordingly. Most of the databases I see are neglecting to include size but
http://www.nintendolife.com/forums/nintendo-switch/nintendo_switch_game_file_sizes?start=60 covers a decent selection of installed sizes,
http://nswdb.com/ has "imagesize" in gigabytes but mostly for untrimmed ROMs (if they are padding out to 8 gigs and the thing is only 5 that is a significant chunk of space). Sizes vary a lot there but 30 gigs is on the high end and it rapidly drops to around 4 or 8 for the less intense games.
Memory wise 512 is not ridiculous but it is not trivial either (probably around the price of the device or a few games). 256 is about half the price of the lower price 512 GB carts, 128 is being sold for next to nothing (SD cards are better than they were but still not good and a 512 gig failing will hurt).
