Apple Extended Keyboard II models are still around, some will need retr0bright treatment but they're good keyboards, if only large and big enough to be sized up to a barn door.
An ADB mouse is something I'd keep on hand for it, but the USB optical mice are WAAAAY better than any of the old rodents. For that thing, I'd also get a decent video card and USB 2.0 and FireWire card for it. You won't be able to use USB 2.0 in pre-OS X software. Aside from Option-key boot selections, I can't think of any use of a non-USB rodent that would be necessary for enjoyment of the machine, though -- but I'd have one just in case -- they're cheap and all over the place.
Add those things up, and the PM G3, particularly with a G4 processor swap (I've heard of 1GHz Sonnet cards for them) and plenty of RAM to go around, are pretty good machines, aside from the ... "meh" ATA bus. With the integrated Zip drive (I'd upgrade it to a 250MB if possible), FDD, DVD drive, expandability, they really are quite flexible.