I just got my SE/30 powered back on earlier today as well. Very excited to get it set up.
However, in response to your question about memory and OS: my SE FDHD has 4mb of ram, and I find 7.1 to be the best balance of ram usage vs features. 7.5 was taking up a noticeable bit more without any of the extra add ons that I have with my 7.1 install.
My SE/30 is sitting with 8mb right now (8*1mb). I'll be setting it up with 7.5.x. That said, I also have an Ethernet card to go with it. IF I can get that to work as well, then I will be switching the 1mb sticks for 4mb sticks giving me 32mb. Any more and my understanding is it begins to take a long time for the system to do the memory check at boot time. Since there is no Sleep mode, that may be annoying. Really boils down to personal preference.
As for games and apps:
Lido (disk utility. It's companion app, PMount allows you to set which partition to be the boot partition. Handy for a single disk multi partition setup. System Picker may be able to do this as well)
ShufflePuck Cafe (fun game with decent sounds)
Background (extension for B&W macs that lets you set a background image... Uses specific MacPaint format, so a little work required to convert images, but I like it)
SuperClock!(basically gives you 7.5s clock in 7/7.1... Maybe 6 as well?)
Moire cdev or After Dark 2.x (I enjoy these two with my vintage systems. Moire cdev is especially light on memory, supports hot corners, and can add a clock as well. Handy for system 6. Really any screen saver though. This is semi important)
... More to come to this list in a few days.
And for good practice, find a label maker and print out the date you installed the PRAM battery. Stick this label to the back. Changing at 5 year intervals will avoid the vast majority of battery leaks.