Another tip which I forgot:

Don't use Open Transport! It uses 2-4MB of RAM, and doesn't give any benefit for 68K Macs.

I'm not a big fan to using a PPC upgrade card to speed up a 68K Mac, unless you've already got one, and want to play with it. IMHO, you'll end up with a slow PPC machine that can easily be beaten by a cheap Nubus or early PPC Mac.

The challenge is to make your 68K Mac as fast as it can be as a 68K Mac!