i bought a 110 link erv1 back in the day on my f4 (should be same as 01-03 f4i). worked on my -1/+2 (i think it was 110). I had about 3 or 4 links extra. but i also did it in such a way that the wheel was closest to the front to give the chain ample space in the back to stretch w/o removing an extra couple of links.
but if you can get a 120, that's fine. i'd go for erv3 or ek chains. (can't remember which EK but some racing buds of mine use that).
kits are not badly priced, but i've done better getting individual ones but i did have to do some searching. try planetracing and white buffalo for the chain prices. they're the best i've seen recently. for sprockets, depends if you want an alloy or steel in the back. i like afam and vortex myself, though there's some nicer ones out there. my sprocket specialist was a so-so, seems to wear out fast back on the f4i. but my vortex on the gixxer, jeez, it looks like it's not even wearing and i compared it against a brand new afam sprocket and the teeth are good!
"Leaders are like tea; put them in hot water to find out how strong they are." Anonymous