seeing as no one else has answered your post there are many options out there. a lot of guys will refer it to upgrade the bike in stages, so lets say Stage 1 would be installing an intake, exhaust and some form of fuel management, for fuel management the best options appear to be either a reflash, a power commander v, or an Aracer Ecu. there are more options but those are the 3 most popular.
if you do the reflash it'll raise the AFR and rev limit of the bike in the stock ECU, a lot of people would then go to a power commander to make fine tuned adjustments after that. Usually this option is done with the stock bore or small bbk's... if you plan on doing a larger bbk there are a lot of options, the most popular being 170, 181, 183 and for the crazy guys the 210. usually for these the best option would be the Aracer ECU Replacement.
Now on to stage two, this is just adding a cam to stage one and getting supporting mods on the bike preparing for stage 3. Supporting mods for bbk's would be an aftermarket cam chain tensioner, heavier clutch, aftermarket clutch case/cover with oil ports for an oil cooler, oil spinner delete, and if spinner is deleted a crankshaft support bearing for the flywheel side of the case. also a high flow oil pump would be needed once an oil cooler is added and if you're gonna be doing wheelies there is one for that too!
Alright stage 3, this one is just installing your big bore kit and tuning, the rest should already be done, all you should have to do is install your piston/jug/head/oil cooler then tune.
If a big bore kit isn't enough for you, another option is a 300 swap! thats right, the cbr300, cb300, cb300f, and rebel 300 can be swapped into a grom using a swap kit, or you could modify the frame and weld it up.
Note upgraded suspension and Aracer ECU would be needed, the rebel 300 would also have different gearing and have a completely different tune.
I hope this helped you and if not, maybe anyone else on the forum might stumble along and get a question answered. Currently I am stage 2 with a cam, intake, exhaust, and reflash, about to install a heavier clutch and springs, as well as a cam chain tensioner. still deciding on fuel management atm.