All the official RPGs (WEG, both WotC and the FFG system) have force power based in RNG.
In Star Wars d20 it was essentially 3.0 psionics crossed with truenaming (two of the worst systems Wizards of the Coast ever devised) and vitality point costs. You both needed skill points in a force discipline (like move object), each of which used a different attribute with no rhyme or reason, and had to make a skill check based on that. Better results gave better effect. A feat let people who styled themselves as spellcasters took longer to cast but could do so with less vitality cost. Vitality was a buffer before you started losing wounds and was relatively easy to recover. It was a total clusterfuck but still OP.
Saga Edition was much better. There's only one force skill, Use the Force, that on its on can preform various minor functions (off the top of my head sense surroundings, predict if an action will have immediate bad consequences and lifting minor objects) at no cost (besides the time to activate it) and was based on charisma. A character trained in Use the Force could pick up Force Training as a feat. Force Training gave you 1+wisdom mod (min 1) powers and could be taken multiple times. Each power was an ability you could activate one per encounter and its effectiveness was based on your Use the Force roll (for example with Move Object your result determines how much you can lift and how much damage it does when it hits something). You could use the same power multiple times by taking it multiple times and later books published special lightsaber fighting techniques that could be used the same way as a force power. Essentially the limit was fatigue and greater force users had greater reserves. This I feel is the easiest to manage in play but 1: All the best stuff for force users is in the core book, with stuff in other books being nice extras at best, but everything else in core only had much lower power level (essentially force users have a much higher skill floor but decent charop greatly balances everyone) 2: It doesn't really support unusual calling on powers you didn't know you had and weird situational powers, which happens all the time in Star Wars (my suggestion is to take a page from Mutants and Masterminds and allow a force point to turn any power in your suite to any other power you don't know, possibly with a penalty on UTF rolls).
I don't recall there being a limit in FFG's system except that as a starting force user you had a very good chance (7/12 or 58%) to fail unless you went dark (then it was 42%) until you got an extra force die (then you got multiple rolls and substantially better odds of some effect). I forget exactly how WEG games did it exactly beyond force powers .