the usual strategy with vaulters if i may says so curedly is to ♥♥♥♥ off to the 4 corners of the galaxy, bonus point if it's in isolated system and pasively win a science victory, of course you can start in a system nearby your spawn for initial research and exploit

Depends on the map and your settings.

If your going for passive science victory. Your looking for systems that will have the highest population after being fully developed.

If your going for aggressive early game. Your looking for chokepoints. By controlling 2 choke points no one can settle in systems between those chokepoints. If they do choose too settle between chokepoints you just teleport a fleet in and take over newly colonized systems after they finish.

If you want too population shuffle. You take a system, build a portal shuffle its population too whatever system you want. Once the population has been emptied trade or give it away too an ally. You do this too stay under system threshold while having all your systems full. You enjoy having 20 of a pop and having 1 of it in every system for multiple minor and major civilizations.

Example you see a 18 population system, you take it then spend 6 turns shipping its population too your other systems. When enemy fleets show up, you either let them take back their 0 population system. Or force them too declare war on the civilzation you traded or gave it away too. You have too fully control the system too do this, most of the time they retake an empty system.

I think the most important thing is to stay in their colonziation cap, the 30 ish percent bonus for doing so is quite nice and takes a lot of tech to be able to go past that without doing more harm than good.

Then use privateers to blockade potential systems as you are scouting like crazy and grab the best ones you find as you are able to colonize. I usually only go for 5 planet systems unless it has really good resources.

well, in general I'd advice to look for
strategics
no less then 4-planet
warm enough to populate and develop before you speedrun the science vic

you can occasionally skip one of those, but in general anything without all 3 is a waste of time and resources, in my experience
another great method of "colonization" is just send argosy towards the galaxy center, find the cluster of minor factions, teleport your fleet in and consume every1. You will likely run into colonization cap way before you run out of minor civs