What I have done with an iMac G4 700MHz like yours:
i) Open it up and give it a good spring cleaning. After a few years the amount of dust & debris that collects all over the logic board, the fan, and frequently blocks the air exhaust at the top, has to be seen to be believed. During re-assy, repaste the CPU and heatsink.
ii) Max out the memory to 1GB.
iii) Change out the hard drive if it's noisy or troublesome. (Note: these are 3.5" IDE).
iv) Perform a few performance tweaks: disable dashboard/spotlight etc. See link
HERE.
v) Do a clean install of OS 10.4 Tiger, and bring it up to 10.4.11
vi) Download TenFourFox - you'll need the 7450 G4e version (this will be 7450-FPR5), and then perform the amazing performance enhancement tweaks detailed
HERE. Imho the simplest would be to implement the SpeedyFox addon, but I prefer to use the user.js option. All is explained
HERE.
Then if you wished to add a new flavour and icing onto the sunflower cake, just download the splendid
Tiger Sierra Theme.
All the above would be a pleasant weekend task, which I'd gratuitously participate in if you were anywhere nearby. Such is my love for these wonderful, truly classic iMacs.