A lot.

With 8 in the RV, the key to making it work is lots of interactive play. We work from home, and I'm (now) great at using wand toys in both hands though I am FAR from ambidextrous. Thankfully they are all older now (our youngest is four), so they are GREAT about taking turns playing, and no one's a play hog. Unless we have to head out for work, they get a minimum of 1/2 hour of dedicated play in the morning and evening, usually 2x at night, and often in the afternoon.
Three of the kitties will play with each other at various points. Four of the others only play with the wand toys, and they really need it or they take out that pent up energy on other cats and get pissy and hissy. Skipping a day here and there doesn't seem to hurt when we've got long days... but thankfully those are at a minimum now.
We used to worry about them if we were gone for an 11 - 14 hour day (which happens rarely these days). But we always came home to them sleeping and not mad at us... so I no longer worry, but Gary frets about everything anyway.

Five of them are very demanding about pets, and it's just easier in the evenings to lie on the bed and watch TV or work on the laptops there, because then the kitties that like to lie on us can do so (after getting the requisite brushies), but there's still lap room for those that want to be on us being petted. We're usually ensconced in a few cats.
In about 1/2 an hour, Gary will be a kitty train - with Lazlo snuggled up on his ankles after being a total spaz while being brushed; Flowerbelle will be tucked in around his knees (and she's not big into pets on any kind of schedule), and Shelly will be on his lap demanding to be brushed (he's a brush hog). Spooky will be inbetween us, getting up THE MINUTE someone isn't petting her, though she prefers being brushed, and we coax her back with.. "Aw Spooky, c'mon!"

Billy will run in and out, wanting brushes and pets for a few minutes here and there, and at some point Ming Loy will come barreling in here, and flop her way over to me and just bust her way through whatever it takes to get on my lap. WHY she won't use Gary's, I don't know, but I am insanely allergic to her drool.

Chumley needs dedicated play time. He gets at least an hour a day on his own, ranging from 5 minutes to about 20 minutes at a time.
