Re CFI Weight :
The limitation is diven by the CG/Total Weight issues associated with the R22. For other training helicopters the issues aren't always that bad.
However, the R22 is the most common training helicopter and as such if you can't instruct in it you limit job opportunities for yourself.
In an R22 I'd say a good weight for an instructor is going to be around 180lbs. Much more than this and you won't be able to accomodate all the students who turn up. I also know someone who although having completed his IR training in an R22 has found that none of the local examiners are able to check him out since his and their combined weights are too high...
r.