I have SD cards lying around, but no M2 cards.Regarding memory, you could always use M2 cards via an adapter which are officially supported.
I won't be doing anything like that, so I should be safe then.what are all the possible causes of a brick?
Usually bricks come from people trying to put a custom firmware for the 1000/2000 on a newer/incompatible PSP, custom themes back in the day, generally playing around with things on the psp nand you not sure of.
a PSP 3000, Using Pro-B10, and with a good speed Micro SD card(s) in an adapter should be fine.
I'll only really be using the PSP for playing games from ISOs and PSX emulation, and won't be messing with system settings I shouldn't change, custom themes and stuff like that.