Good story sopp and just so you know I had no trouble understanding you. I love these little bumblebee toads. I'm glad that you took the time and effort to nurse him back to good health and from the looks of the pictures, I'd say he looks pretty normal.. (comparing to other pictures I've seen of them). As far as how many fruit flies to feed.. I'd probably offer the 20 like you said and go from there.. if he eats them all and wants more, why not offer a few more? I don't own one of these toads but with my frogs I've noticed they know when they're full. If this guy is finally eating on his own he might have quite an appetite so I'd offer him as much as he can eat, I hear these guys can have voracious appetites.
Also, that vivarium is gorgeous. What a nice home that toad has, haha. I don't think I could ever build a Viv that good looking.. I still haven't tried.. one day.