I do believe you got it.

I have never tested the different configurations to see what gave the most / least planets etc, but what you described is pretty much what those options mean.

So for instance, without changing planets from abundant, you will have a lot fewer planets to colonize if you just make suns rare.

You will also have a different number of planets and stars by changing the option for clusters. That is tight, scattered etc.  I think you actually wind up with more planets if you play with scattered. Personally i like tight because it makes the use of economic starbases better, since you'll have more planets gaining the bonuses.

Im not sure if the "Random" option will make the map have some loose and some tight clusters or if "random" means that the game will choose a single one for you.  I'm thinking is the latter, but anyone who knows can chime in to verify / correct what i said.