Possible tack: Enough material was sent for one Colony to establish itself quite quickly, but the group fractured, leading first to sub-colonies (which are a couple of orders of magnitude less well equipped than the first) and then to their rebellion.

When I say Earth is far enough away that it's irrelevant, that might only need a few years of travel time, maybe not even that much. Enough for this all to play out before a message could get to Earth and Ships could make it back from Earth. Depending on the timescale you need for the story, it could even be a matter of months rather than years.

OK, I think I'm stuck on this idea for now. If you want to play with it further, I'll go along, but I'm not sure I'll be of any use for a while on other directions :P