I agree with naturalpasture on the four week schedule. Also make sure your farrier knows how to do a barefoot trim since it is a lot different then trimming up for a shoe. I do all my own farrier work and have no issues with cracking. If I procrastinate to long my appy will chip off on the sides but never crack. As for my mustang, her hooves are living rock, so cracking and breaking are unheard of no matter how long.
A barefoot trim leaves less wall on the outside so their sole helps with support. First timers tend to lame up a bit because they are like humans, we need to get used to going barefoot, some horses are tender footed and need shoes or boots for rocky terrain so keep that in mind.
The hoof should have a nice concave bottom, but the walls should not protrude down and be the only weight carrier, that would cause cracking. The heal is cut down level with the frog and the front portion of the hoof is rolled up. If you ever do have a dry spell pine tar and vegetable oil in equal portions stays on very well in the pasture and moisturizes the hoof, as well as being much more affordable than other methods(your farrier will thank you for not having to trim rocks).
I recommend getting a hoof rasp and having your farrier show you how to use it. If you touch up the round edges and clean up the hoof a little between trims that can also help. Make sure its sharp. Its all about the pressure you apply. Apply to much pressure and you can’t move the rasp, to little and nothing is shaved off.