A few suggestions:
Don't go for a giant population system (high millions or billions) if your group is new and small. You can always expand into those but you don't want your home system to be a nightmare to take in the first place.
Be sure you check out your surroundings for your desired system. Look for how populated the area might be with other player minor factions. This is actually becoming harder to avoid but try to give yourself some expansion room.
Check your Power. Powerplay powers have certain government types they are favorable, neutral, and unfavorable to. Try and choose a govt type favorable to the power in your area, otherwise the power is likely bigger than you and will beat you into submission. (I know this because I do it, and I hate that FDev makes me do it but never the less, it is what it is)