1. Create a new @2540 wallet on an offline and provably cle…

How durable are SD cards?

I certainly would _not_ rely on SD cards or USB drives. @1850 's suggestions are great, but you can also do the same thing with an offline/old Android phone and a fresh ROM like LineageOS and Simply Cash. Regardless, protect those seed words!

What's bad about them? I figure a phone or any other hardware device would use an SSD nowadays.

SSDs are a fair bit different than cheap flash storage like microSD / USB thumb drives. There is a decent article @ https://www.maketecheasier.com/sd-card-vs-ssd/ which explains a bit more.

If you're going the route of an offline PC, don't install your OS to a microSD or USB drive. I would use a proper SSD or even HDD at worst case. If you install Linux, you can setup full disk encryption too.

For this use-case, a Live USB drive is ideal as you're not looking for file persistence ;) That is, if you want your storage ice cold.

Of course if you're running any OS as a daily driver, a good SSD is recommended.

It really all depends on your desired use case. I.E. if you want to make it easy or tough for others (family, etc.) to recover your coins in the event of an emergency. Hope I helped somewhat, but it's tough to explain a lot in such small posts.

How about using a Raspberry Pi as a semi cold storage, that is mostly offline? Also what exactly do you mean with a watch-only wallet.

Alright, thanks for the infos. One thing I still wonder about is: is just saving the seed phrase sufficient to recover the wallet in the future? Or is it better practice to save the key.

At present, the 12 word seed phrase is still the de-facto standard for wallet recovery. Make a few copies on quality paper, laminate 'em, and put them somewhere safe and you should be good.

Just be sure to hand-write your seeds, don't type them anywhere!