Your weight should never be a problem for horses and ponies as chances are they can carry about 3 of you no problem. For leg length, basically as long as you can give him the aids properly then it's fine. Ideally your legs should be in line with a horse's belly, but as long as your heels can make contact with his sides, you can easily get a secure lower leg and it's perfectly fine to ride that pony.

I am nearing 6' and I still ride 14.2hh ponies from time to time, just with quite short stirrups