I had a 64GB SD card on my surface pro 1.
It's fine for storing stuff, but doesn't use it as a main storage for downloads and documents, because SD cards doesn't like multiple access and can get painfully slow.
Download to the internal memory first then move to your SD card, and when consuming from it, make sure there's no one using it.
I know it's tempting to put the onedrive folder on the SD card, but trust me, it's not a pleasant experience
On the other topic, like Tap Tap, I also don't use a cover, I would only recommend a sleeve or something like it if you are tossing it in a bag were there's other stuff that could scratch it. If your bag have a dedicated compartment not even that is needed. Just be careful, the tablet is sturdy enough to be even dropped from your hands on a carpet and not even have a single scratch, but it might dent a little if it falls on a hard floor on the edges... Oh, and a general usage advice: Always try to keep in mind that the "balance point" (not sure how it's called XD) of the device when it's opened like a laptop is on the kickstand, you might end up letting without base which most likely will cause a fall (happened to me with my S1, that's how I know it can fall from a desk and still work
)