Hi Serano!
Welcome to cheese making! don't worry about mistakes, it's part of the game.
15 minutes for rehydration is a bit long. If you managed to stir and wait 5 minutes before adding rennet, then you might be ok. Some recipes (such as Caldwell's) only require 5 minutes of ripening. I`m not sure you`ll get proper acidification though. Only time will tell.
Long time before cutting happens. It just means you may need to adjust your rennet quantity as rennet looses potency after a while (especially liquid rennet). Check out the forum for something called "flocculation Method". It takes the guessing out of proper coagulation time.
Air drying at 35C and 10%RH is really not optimal. In reality you should be closer to 12-16C with 70-80%RH with some air exchange but no air current (wind). Most Home-Recipe books will suggest air drying at room temp for convenience as 12-16C is hard to achieve at home. Your low RH% explains the crack that appeared after 1 day of drying; the rind dried much quicker than the paste. By putting it in your cave, you probably saved it! Nice one
just keep an eye on RH and try to keep it above 60% while air drying.
If you open your cheese at 2 months, you be disappointed. 2 months is a bit young for a cheddar as it`s still under developed.
This is all I`ve got. Maybe someone more experienced has more in depth insights. Hope it helps though.