How much inside shot/inside defense is enough? ~10?
Depends on the offense and defense you plan on running. It seems you're building inside oriented guards so yeah 10 is a start for IS.
What offense best utilizes driving guards? Will zone defenses help against driving guards? Will the bigs with great ID and SB pick up on them as they slip in?
1. Look Inside, Isolation and Princeton to an extent.
2. Zone defenses will help more than MtM yes.
My understanding is Jump range is not very important. Maybe get passing to the 10-12 range.
Again depends onthe offense. Inside? Sure don't train JR at all (and JS to an extent) You'll definitely want passing.
JS (16), OD (14 would love higher though), DV (16), IS (6-10), RB (idc), Stamina (5?), JR (n/a whatever JS training brings it to), HN (16), PA (10-12), ID (10), SB (N/A), FT (8)
JS might be a tad high for what you're trying to achieve with their potential
Also my understanding is stamina will train regardless of age, but is this at a reasonable speed? What about free throws?
Stamina and Free Throws training speed are not dependent on age but they do not increase with age. In fact Stamina diminishes
Is it possible to train your guys until they cap and then train some stamina/FT the next year (if all star break and playoffs isnt enough) and then get trainees the following year, or will the skill cap effect ST/FT speed?
Yes, those two aren't really bound to the same rules as the other skills. It's better to cap them then train ST/FT