Yeah I've been thinking about going for a mix of physical and digital for this.
Same boat here. Thinking of going primarily physical, but I'm sure I'll want to download certain titles that I know I'll play again and again on and off. So for example I'm buying Zelda physical, since I will only rarely replay it later, but will buy Ultra Street Fighter II digital since I kind of just want to always have it on there when I feel like playing it for a while.
As far as size goes, both the 128gb and 200gb cards are about the same cost per gb so long as you find a good deal on the 200gb one. Amazon and Best Buy prices are high on the 200gb card right now, but Adorama and B&H have it for $70. That's almost the same cost per gb as good 128gb cards are at $40 ($.35 per GB versus $.3125). Given that, I'd go with a 200gb card if that price difference now isn't a big deal knowing you're paying the same cost per gig.
If I didn't already have a 128gb lying around I'd buy a 200 now. To me that feels like a pretty large difference in size for the same cost per gig, and given that most games are going to be around the 10-20gb range with the occasional outlier at 32gb should be enough to hold basically everything for quite some time. Another thing to consider is if you have any use for a micro sd card besides your Switch. If you don't have anything else you'll use it for, I'd go with a bigger card now... since whenever you upgrade for more space down the line you won't have a use for the smaller gb card anymore.
