Malkorian

In the mod I linked, it enforces an 'upkeep' system where each summoned creature has an initial mana cost to cast the summoning spell and then requires another chunk of mana which is removed from your total for as long as the creature survives - which could be indefinite. There is also a hard limit to the number of minions you can sustain, even if you had an unlimited supply of mana. This limit is increased significantly through perks and the upkeep costs are also reduced through perks. It seems to be exactly what you are describing...

What you are describing sounds a lot like this: http://skyrim.nexusmods.com/mods/25024

I've searched without success for a mod that does what I am thinking of. I have always hoped there could be a way to take control of different characters once they are added to your party and use them in different situations as may be required. For example, the main character - the dragon born - might be ideal for leading your merry band of adventurers but he or she can only be skilled in so many fields. Maybe they are a great warrior but you suddenly need to sneak through a dungeon. Well, you happen to have a stealthy companion who is up to the task. Or you might have a double-talking imperial ally who can get you the best deals from the merchants, so it is better to let them do the talking when it comes to pawning your loot. Anyone know if this is feasible or if maybe I missed it and it was already done? Thanks!