I don't know much about motorbikes, but traditional car alternators use RPM and vacuum to advance the curve which should be easy enough with arduino. RPM alone from a hall effect sensor should be enough to get you started. I'd go with the ignition first and then the injection. I wouldn't try to calculate the mix so much as tune in a practical way based on experiment. Hopefully the arduino will cope with the lookups at the top end.
I suspect that you could get the bike running with RPM sensors alone.
Sounds like a cool project but I think it'll be an uphill battle to get good results.