No need for the express card just yet. I havent bought many digital only games on SW2 like I still do for my SW1.

Nope. I get most games on PS4 and PS5 so I have a smaller Switch and Switch 2 library of multiplats. And since I get most retail games physically, I still have over 100 GB free on Switch 2 methinks.
Mario Kart World doesn't take up much space, nor do some of my other digital games.
I'll probably get a microSD Express this year, but I sense no urgency.

Don't need one. I only buy physical for consoles.

Yes, bought 512 GB each for my partner's and mine in October. Basically have gone full digital outside Nintendo's first party games. Been very tempted to sell my physical copies and go pure digital for Nintendo games too, for the convenience and the fact that I am practically digital only on all other platforms too. I am not much of a collector, and don't care much about resale value anymore. 

512GB card. I have like 200GB left.

No. Physical only, so only thing, so far, that's actually on Switch is MKW from the bundle, updates and upgrades of SW1 games.

My Switch 2 was already full with all my Switch 1 digital games on launch, so I've been on the lookout for the expansion since then.

I got a SanDisk 512GB end of November, as it was one of the first times I noticed it on sale.
Would have preferred a Samsung card as I had good experience with them, but only SanDisk was available then.
1TB prices were prohibitive and from brands I would not trust (https://de.camelcamelcamel.com/product/B0DXKQHB7D).

Bought it for 90eur, it's currently going for 120eur (discounted?) with an RRP of 160eur !!!
Price evolution: https://de.camelcamelcamel.com/product/B0DTQ35NH6

I see this Samsung one is stlll available at a reasonable price: https://de.camelcamelcamel.com/product/B0FTSXX7QR

Nintendo should allow us to add an SSD to the Dock and whenever you want to play those games, I just copy from SSD to the console.

I have a 256GB, probably upgrading to a 512 sometime later and handing this one down. I doubt I’ll need a 1TB.

But there is this one (Canada) which is 1TB for 150 CAD (about 110 USD) which would be effectively doubling the space for a relatively negligible amount more. Out of stock, and I don’t know anything about this retailer brand card.

https://www.ebgames.ca/Switch%202/Games/938876

Dont have Switch 2 yet.
Waiting for Xenoblade Chronicles 4 and graphic upgrade for 3 and especially 2,
But i think 1Tb is minimum since updates are nowdays almost as big as games.
Also price here is insane, 500Gb cost more then Switch 1 new :D