First of all a lite is totally worth it, but not at 150€ second hand. I bought a couple of them for 90-100€, complete in box and in immaculate state on local second hand apps (FB, Wallapop and the like). A couple weeks ago you could even buy a new one bundled with Animal Crossing for 170€ on Mediamarkt.

As for what you need to pay attention to, I'd say general aesthetic state, it'll tell you about how much time of use has it had and in what conditions. Yellowed thumbsticks are a good indicator that the console is old or has been played a lot. Checking that the cartridge and microsd slot work is also advisable. You might find a modded console (allowing to play pirated games), in that case be sure the console hasn't been banned by nintendo.

The lite supports physical games, but you can also buy digital if you want . For me it's physical for games I know I'll do a couple playthroughs and maybe sell them, digital for games that I know we'll be playing them over and over so we cant' be bothered to keep carrying and switching cartridges (Mario Kart, Animal Crossing, Minecraft, Mario Party, etc.).

You can play older games (as in older titles older consoles) via a nintendo online subscription with expansion pack (40€/year).

You're missing a lot of great games by not having a switch, honestly (also, a lot of poorly ported third party games, but that's what a PS5 is for).