Hello wow. Excellent questions.
I think you would be fairly safe with that scale. 300 grams is actually a little over half a pound and most chameleons don't weight that much. I can't seem to find my notes on the Jewelled rudis (they are slightly larger than the regular rudis) I kept, but some of the closely related species I work with range from 30grams to 50grams when gravid.
I use Susan Donohue/Walkabout Farms "Montane Shade" on my chameleons daily but I'm afraid it might not be available anymore.

It is a shame because I really don't feel the more common supplements (Rep-cal, Minerall et.al) are near the quality of the Walkabout Farms formula(s).
I believe the rudis, and their closely related brethren, can be kept in groups. They seem to have a much more calm demeanour than some of the larger species of chameleons. Depending on the individual specimen though, there are points of the year where I can not have them live communally. In the wild, they can escape from amorous and/or aggressive males if needed. In a cage, no matter how big, they can't. There is certainly nothing wrong with admitting you are hesitant of housing them in groups (in fact, I really respect that

) and in the case of the rudis, housing them individually is not necessary and will not harm them. I don't think there is any psychological or physical need for housing in groups with the bitaeniatus family.
The rudis are a nice, small, underrated chameleon and there are plenty CB specimens available if you are considering them. Avoid WC's!
Good luck.
Trace