Okay, one more related question - is there advantage of two CMDRs doing 50 missions each over one CMDR doing 100 of those same missions?
I've been able to expand one minor faction across ~10 systems over perhaps 3 or 4 years. At times I suspect some other CMDR(s?) have also been actively supporting the same faction, but I've not yet detected them (I suspect it's just how INF moves at times in a seemingly deliberate manner that I would have perhaps chosen).
Actions - best to do a little bit of everying, not just Missions alone (but for Missions, focus on the higher INF ones, +++++ or ++++), but also Bounty Hunting (can gain bounties by using a Kill Warrant Scanner, even if your chosen faction doesn't control the system, you'll pick up some bounties too), Trading (only if the faction controls a Commodity Market), Exploration Data (only if the factions controls a Station). Each day/tick I try to do a little bit of each. Plus, that's better variety for me. Optimal ship? Well, each to their own, but for BGS I tend to prefer the Python. Can handle combat, land at outposts, complete all mission types, and haul 128T trading (in my fitout).
I hope that helps, and good luck with your BGS adventures.