Prior to this expansion, the rule was to expand as quickly as possible.
In the recent expansion, my experience with pre-warp starts is that slower expasion is required. Money is very tight, you have to watch how much you build and develop some economy before starting to expand. New colonies are a cash drain initially - it takes time for them to start producing money and much longer time to produce a payback.
Even within your home system, I don't colonize until after post warp. You can't defend the colony and it is a cost drain. If the pirates are raiding, then your initial investment in a colony or spaceport can be destroyed in a raid. So I end up sending a transport with six ground units to land right after the colony ship to provide immediate defense, put a fleet of six to eight ships around it until the spaceport is build. Also, in the prior expansion, small spaceports were built with minimal structure - in this one, they have to be relatively strong to fend off pirate raiders. All of this increases the case initial cash outflow.
I'm not saying this is the best approach, but is what is currently working for me.
And I used to target virtually any world over 60%. Now, at least initially, I target worlds over 80% in quality unless they are in my home system.
So expansion, for me, has moved from an explosive race, to slow, controlled and deliberate pace.
In keeping with this keep cost down strategy, I don't build research stations. Instead, I add research labs to my home spaceport. Initially, I modify the small spaceport design to have 12 labs each of high tech, weapons and energy. When the economy up and going, I will retrofit this to large spaceport with 15 to 20 labs of each. And I don't build defensive bases at my home port but rather load up the home spaceport on the second or third retofit and later with lots of shield, armor and weapons to create as good a fortress as I can. Again, this keeps cost down over the long haul.
You have to control expensives in the game and plan for colonies to take about 5 to 10 years to become "cash positive" after the initial investment - which includes the colony ship, the spaceport, the home guard, and any permanetly stationed fleet to defend it. In other words, a lot of money is tied up in the colony - add in losing money to pirate rates (which will happen), and a new colony is a BIG investment.