Fantastic - love these machines, really miss mine even though it was knackered and I eventually got rid of it due to lack of room.
There's plenty of stuff on the web about the SE/30 and the simpler Mac SE, eg The Mac SE Support Pages
http://www.ccadams.org/se/
and of course Low End Mac.
You can up the ram to 128mb if you can find the RAM [when I sold mine off I think someone was using it in a laser printer].
http://lowendmac.com/2016/memory-upgrades-mac-se30/
Also you can add a choice of cards to the internal slot, they still come up on ebay from time to time
Not too bad to do the internal upgrades, though seem to recall getting torn up a bit due to the tight space.
I also remember having a SCSI ribbon cable hanging out the back of mine to add a SCSI CDROM. I daresay there are proper external solutions; I probably only had the ribbon cable at the time.
There were also cards for external monitors - vertically-oriented A4 monitor and maybe a colour card?
Trouble with all this stuff is finding it of course, it's a lot more scarce than it was. There used to be a dealer in the US I bought bits from - olde-mac-milt - but looks like he doesn't still deal.