It was not mentioned here but you should hardly ever build your infrastucture very far in advance. Don't just build 8 city districts when your planet has a population of 3. This is because districts and buildings never (or almost never) give their bonuses unless fully staffed, but you still pay upkeep. And the upkeep costs are likely to strangle your economy if you let them baloon with no purpose.
For basic planetary management, do 3 things. Is housing positive? Are amenities positive? Is unemployment between 0 and -1 (That is, no unemployment, and maximum 1 empty job)? Then that is a well-run colony. (There is quite a book on advanced planetary management, but if you keep the above 3, you are doing better than average).
As to what to colonize, it is true that you, in general, want to colonize everything. But there is a nuance. Planets are divided into habitability classes. Without getting into the really gritty underbelly, there are 3 types you care about at the start. Of which, two are your targets, M class and L class.
M class have a habitability of at least 80% and are shown on the galaxy map as a green dot. These should be your first priority.
L class have a habitability of between 50% and 80%, and are shown as yellow dots. These should be your second priority.
Brown dots and under should be avoided until you finish with the rest, though there is an argument to just wait for Terraforming technology instead.
Reason is that habitability impacts pops in negative ways. They eat more amenities, more housing, reproduce slower, and suck at their jobs. Even an amazing planet in theory with good synergic features, with low habitability, will struggle and barely plod along. Even with mountains of focused investment, you are likely to maybe break even with upkeep, if that.
In short, I would say that if you build a colony on low hab planets, give them some basic med clinics or smth, and once it grows, relocate extra pops to more productive planets, and make investments on those instead. Any investment you make on an even amazing low hab world will take ages to recuperate, assuming it gets recuperated at all and not just eaten up by upkeep.