M.D.
Children will generally let you know when they are ready. The fact that he can see what he does is great. I would try the new pampers feel and learn diapers and see how that works. I've heard it works wonders. Other than that I just use the 10-min method---after a drink ( a full drink), wait roughly 10 min, sit him on the potty turn on the sink to a trickle and let him sit it out until he goes. Normally 9 out of 10 they go, repeat this method several times and he'll get the hang of it.
Mom of 4.