I have weaned at five months before. I did it because the mare could not hold her weight. The mare and foal had been in a double paddock that had two stalls and we just put the fence back in the middle of the paddock. That way mom and baby could touch noses anytime they wanted to. There was no stress no fuss. The only thing about this is if momma is still wanting to nurse the foal (and it sounds like yours is done) she can lean against the fence and the foal can nurse through the fence.
Personally, I like this way because there is no stress to anyone. If your mare is uncomfortable, yes, don't ride, but don't be so sure she is uncomfortable. If she is already startign to wean the baby, her milk production is already going done. She was definatly appreciate being takin out for walks or light riding. I don't think I would take her for a six hour trail ride, but an hour of playing should be just fine.
As for gelding the colt the answer is it depends. If you are at a boarding stable, they may say no ungelded colts over ______ age. I have seen that age as low as six months. If you want a thicker horse, geld later - like two years. If you want a taller horse, geld sooner, six months will be fine.
If you know you are not going to keep him a stallion, geld him before he annoys you. I had an Arab colt who at eight months turned into an absolute idiot. I was not going to keep him a stud, so off they went!! A month later he was back to sweet and great.
My current gelding we kept going back and forth on if we were going to geld him (and hind sight being 20/20 I wish we had kept him a stallion) we finally gelded him at two only because I was having trouble finding boarding stables who would have a stallion in full care. Because he went so long, even as a 14 year old gelding, he has a lot of the looks of a stallion. Personality wise, he was a nicer stallion then gelding - and for those who will poo poo me about saying I should have kept him a stallion, look up Norsk San Diego - my horse's full brother - and get back to me...