6. Mind that Bounty Board!
PlunderNauts Guide
It may not be obvious but the Bounty Board is at least as good a source of income as planets are from a passive PoV.
The bounties on offer are constantly changing, and they often pay for things you will do anyway, so keeping an eye on - and claiming any you have completed - is just good business. After all it is free money - but only if you are paying attention and remember to check it and claim any that are due to you before their timer runs out!
Another point in their favor is that Bounties are the best way to earn larger amounts of Antimatter!