For my games, I treat a Force slam as pretty much being the same as hurling the targeted person at the ground. Since most individuals are Silhouette 1, that means they suffer 10 damage plus successes on the Discipline check. Knocking the target on their hindquarters (i.e. prone) is 3 Advantage, while 2 Advantage can be spent to give the target a setback die to account for them being off-balance from the 'throw' and a Triumph can inflict a critical injury.
For minion groups, I handle it a little bit differently. In effect, the Force user hurls one member of the minion group into the rest of the group, so the group suffers two hits of 10 damage plus successes. Now I usually treat my minion groups as being engaged with one another (a holdover from Saga Edition's squad rules I suppose). So as an example, if a PC uses Move to attack a minion group of 3 stormtroopers and gets 3 successes on their Discipline check, then the trooper group would take a total of 16 damage, with each hit being 10 base + 3 successes = 13 damage, less the trooper's 5 soak (as it's being treated as two individual hits instead of just one big one). Thus far, it seems to work pretty well, making a "Force slam" type of attack useful but not completely encounter breaking at the lower end of the spectrum (something that could not always be said for the Force Slam power in WotC's Saga Edition, which could and did end low-level combat encounters in one action if the bad guys were clumped together).