1) Did not know there was a bug so no.
2a1) If taken soon enough after a size increase there are size reduction potions, work on hair, boobs & butt. Also a chance of that happening when using the dungeon altar when it is safe to use (and an 1 in 6 or so chance for hair reduction through the dungeon throne). Keep in mind there is a time limit, once past that the only way is post game when you have more then the minimum amount of money to 'win'.
2a2) Belly depends on how you got there, ranges from starving yourself to giving birth to just letting out air.
2b) options when setting up a new game for maximum sizes, pregnancy excluded due to it being temporary.
3a) Since there are tentacle monsters you have magic enabled and at least 1 magic power. The monsters themselves have to be killed (or removed with a weaken+ attack or disintegrate cheat). The spawner, depending on the zone you are in, takes either 4, 8, 12 magic power to purify. Most likely way to expand magic capacity is killing tentacle monsters, there are some one of events (most if not all associated with the academy), a food, and possibly a potion (blessed magic IIRC) that increase maximum capacity.
Most reliable recharge of spent power is done through the dungeon altar when it is safe to use.
3b) any egg you find is to be destroyed.