Dude, welcome. Here are a few pointers:

1) Don't start your first comment going on the defensive for buying the N900.
2) Don't subsequently call it a 'such an old piece of technology'. Ever!
3) Now as it's from ebay I would suggest flashing it. Start reading the wiki!
4) Follow up by upgrading it to CSSU-Stable.
5) A 32GB SD is nice to have. If you really need the space there are a few comments about compatible 64GB SD cards. Check it out.
6) Get yourself a screen protector as well as the case protection. The stylus will scratch the screen!
7) Be carefull of the USB port. It is delicate. There's a thread by dr_frost_dk that might interest you.
7) Watch out for Dave