[Zeke]

Wire size is determined by the length of run and the breaker feeding it. You might be just fine with #8 on a 30 amp circuit. You don't need a disconnect in the new garage if you keep the breaker count at 6 or less, double pull tied breakers count as 2.

At the garage end, the load determines how many breakers. You do have to anticipate a little more than minimum. One thing for sure, you aren't putting a charging station out there on a 30 amp circuit. There is a mis conception that all the breakers need to be smaller than the feed. Not so, you can have a 30 amp breaker in your new panel. 3-4 20's would be better. 25A really isn't used because 30A will handle a #10. You could ostensibly weld out there on a 30A with the panel being fed by #8 (given the voltage drop at 100', about 6+ volts @240 plus whatever wires, cords are used in the building).

You might consider 15A for the lights. High bay LED's don't draw much current. If all the lights are on a dedicated circuit, 15A will handle a bunch, including exterior lighting. 14 ga is so much easier to work with, not to mention the cost. But if that is going to result in a lot of waste, stay with the 12. You can under protect it, just not over protect it (see the comment about a 25A breaker above).

A 12 space panel is as cheap as they come. Rather than buy a 30A GFCI to feed all this, you could put a GFCI at the head of each proposed circuit with a dead front for the lighting. That way your GFCI's will be right there in the same building. No AFCI needed.