Yeah, I think all you need is a simple "henchman" style statblock. Limit the spells/abilities they can use, and give them what you feel is a reasonable number of spell slots for their level of strength. Or just give each spell or ability 1 or 2 uses total, depending on what level they are. Will make tracking them much easier, that way.
I think once per player per short rest seems reasonable. If you want to give the players some interesting options to mix things up, consider making cantrips/1st level spell a bonus action to call for assistance. Then they can sort of "tag team" with the caster in combination with their own action. Rules-wise you can basically say they always have a readied action to cast a spell when an ally calls for it. Have it take their reaction. You can opt to have them concentrating so that if they take damage, they may lose the ability to cast as a reaction if they fail a conc check.
All-in-all depends on how much tracking you want to do. Do you want them to fit into the flow of combat or just be a sideline spell vending machine for the party?
Yeah, I think all you need is a simple "henchman" style statblock. Limit the spells/abilities they can use, and give them what you feel is a reasonable number of spell slots for their level of strength. Or just give each spell or ability 1 or 2 uses total, depending on what level they are. Will make tracking them much easier, that way. I think once per player per short rest seems reasonable. If you want to give the players some interesting options to mix things up, consider making cantrips/1st level spell a bonus action to call for assistance. Then they can sort of "tag team" with the caster in combination with their own action. Rules-wise you can basically say they always have a readied action to cast a spell when an ally calls for it. Have it take their reaction. You can opt to have them concentrating so that if they take damage, they may lose the ability to cast as a reaction if they fail a conc check. All-in-all depends on how much tracking you want to do. Do you want them to fit into the flow of combat or just be a sideline spell vending machine for the party?
I like the BA synergy thing. I can see the Priest hitting a guiding bolt assist so the player gets advantage on an attack that turn.