Settle the higher PQ planets first - at the begining, most of the cash you are getting is based on the PQ of the planets you colonize, not your pop, so get the better ones. (If I have a choice, I usually dont bother to settle PQ15-17 during the rush - they are backfilled later.) Put 115 on PQ16-18 planets, and 300+ on better ones if you can. On PQ15, I go as low as 1. This will maximize the bc per pop you get.
Build Soil Enrichment, Habitat, and Banking asap (they cost no maintenance, and bring in more cash - do them first)
Upgrade your government ASAP (remember +20% eco for each government upgrade!), and it costs no maintenance.
Be cautious with your military units - recent upgrades make starbases cost 5perturn, and scouts 1perturn - EXPENSIVE! (I don't begrudge the bigger military units, but beware those scouts.)
~SDC~