Upload & Sell: Off
going down the path of providing grip to your clients can get pretty expensive (though I suppose that means you can also increase your rates).
Who is your clientele? If you are catering to portraiture/fashion, I'd think they would expect availability of at least 3-5 decent strobes, enough stands of various sorts for them all (including at least one beefy stand that can handle a decent sized boom arm if they want to use one strobe as an overhead hair light, oh, and the boom arm...). providing a remote trigger would also be good -it solves a lot of potential problems with ground loops, frying equipment due to incompatible trigger voltages, etc. I'm not sure about assuming they have a camera that can actually trigger the lights optically.
Don't know what to say on the monolight/vs pack thing or brand, other than to note you probably should also budget for a hot spare (all this equipment eventually has issues under heavy usage), and to check out the service organization as you -will- eventually be sending the stuff in for repair, and it sucks if they either can't be fixed (Chinese clone) or you have to wait a month to get gear back and they don't have a loaner program.
On the modifiers for the strobes, in addition to a beauty dish/softbox I'd probably also recommend getting some umbrellas of various sorts (often people want several lights to have the same characteristics). You could go broke trying to provide the the other modifiers people often want, though I suppose your clients would be happy if there was a box of reflectors (some of the multiple surface types (5 in 1?)) and some stands/arms/clamps/fingers/autopoles/etc. available, plus some black paper/cloth or something...
If they want to do product work, all bets are off on the grip - it seems like you -never- have enough - and actually the same thing with the lighting for product work - 400w/s often won't cut it for a key light when doing product stuff in a surprisingly large number of situations.
Good Luck with your venture,