Performance parts depend on whether it is an M13 engine or a G13. A 1.6 from a similar age Baleno is a good swap, read up on the 1.6 swap into a Samurai, its very similar, the 1.3 ECU seems to work well with the Baleno injectors. Have a look on Difflock.com as well, there are a good few Jimnys on there, SimonDoc is the man with the 1.6 knowledge. There are quite a few aftermarket wheel options, Suzuki themselves offered several options, usually 7" rims with 95mm of backspacing.
The ECU should be remappable but I've not had a look inside a Jimny one.