1) I go as much by behavior as I do size/weight. Most of my Balls are switched over to 32s around 4-5 months. Once I switch them over I pay close attention to activity level, if they are thermoregulating and of course if they eating in the larger tub. If they dont eat inside of a month, are not really thermoregulating nor being active at all.... you know the larger environment is stressing them. Those that eat well and are utilizing the larger space stays in the larger tub. Those that dont go back to 15s. All snakes are different and will be ready at different times.
2) Some males my be fine their entire lives in a 32. Others may not. Again, it is all about individual behavior. I have snakes that wont eat in big racks like the 41s or the CB-70s. Put them back in their 32s and they eat like no tomorrow. And I have a some snakes that wont eat in 32s, but will eat like clockwork in CB-70s. There is no exact science with these critters. It is all about getting to know your individual animals.
Can you force them to live in 32s all their lives? Sure. Would some snakes do better in a larger enclosure? Absolutely.
All of my older girls are in CB-70 tubs (33" x 18"). It would be laughable to me to try and keep 3000-4000 gram snakes in 32s. All my older girls would be suffering in 32s, they would take up 80% of the tub.
As far as hides, if you are using typical plastic racks that is more or less one big hide. If you think about Balls in nature, they spend 75% of their lives underground in a burrow. Eating the occupants of the burrow and hanging out until the meal is digested and then moving on to the next burrow.
Now with that being said, some of my snakes do like a hide even in the rack. If that makes them feel safe and secure and happy... then so be it. I typically just put one hide in the tub, on the towards the front. I dont put one back by the heat. But most of mine dont use a hide even when they are offered.
I remember a few years ago I went and bought 15 of the 321 Boaphile cages. Thought, "hey my big girls will love having a full 3 feet by 2 feet floor space to utilize". Guess what? 12 out of the 15 snakes I put in those never ate in them. Never seen them leave their hides. We are talking 2 months before I finally gave up and returned them to their CB-70 racks. Whether it was the larger space or the big window in the front, they plain did not like being in those cages. First week back in the racks and most of the snakes ate. The second week they all ate. Go figure.
3) I feed small rats or adult ASFs.