awwwwwwwwww him is beautiful! congrats
1. about 9-12 weeks after he came out of pouch
2. mom will start weening as early as 4 weeks to 5 or 6 weeks from when he came fully out of pouch. Mom and dad will bring him with them to eat, he will likely start eating the staple first and not eat much fruit or veg till he gets a lil bigger. He should be eating normal adult food by about 7-10 weeks out of pouch (oop) and no longer nursing, about then his head should be to big to fit in moms pouch.
I don't know what diet your feeding but any foods mom and dad can eat, is fine for the joey. Treat wise, avoid nuts and seeds for joey especially I wouldn't feed them to adults either.
3. Boys can be neutered at 12 weeks oop. If he is staying in the cage with mom and dad he should be neutered no later than 4 months old, If not neutered by then separate him until neutered.