@Jamppa
How about the OS, do you know if I can install OS3.9 or should I just go for the latest version? (which is...?).
You can not install 3.9 on vanilla A600. 68000 is too weak for 3.9 and you also need more memory and a CD-ROM to install the OS. It is better stay with 3.1 and if you want 3.9 go for A1200 which has better accelerators.
and is it necessary to install anymore than an extra 1MB?
More the merrier but finding expansion boards for A600 is difficult.