How do I tell when my economy is ready for me to expand to other planets?
Thats a huge one - and its at the heart of how to play GalCiv. There's no easy way to explain it - its like trying to explain the taste of Strawberries
Each player has their own style of play, and there are as many "Paths to Sweetness and Light" as there are players explaining the "True Way" in terms of Tactics to get there. At the end of the day, the game is all about the economy, how money is generated, its relative value for the items bought, and the severe limitations of getting that wrong. Its from an understanding of how the economy works that the game flows.
Ignore the economy, or get it continually wrong, and I'll guarantee you'll hate this game with a passion, ending up putting your fist through the screen

. Get into the economy - and it takes tiiiiiime dont expect instant "sweetness and light". Expect weeks of working at it and many, many, "failed" games - and you'll then love it and get hooked for life...
A common problem we all have when starting to wrap our heads around this, is "going bankrupt" within a few game weeks/months. There are Zillions of threads on this, and its worth going through a few of them, a recent good one is :
Economy Thread.
I suggest you select a map layout that you like, save it so you can restart it, then practice the early game over and over (up to - say - the first game year or so), restart it, practice the early game again etc. That way you do several early games a session and get into it quicker. Its all about the early game and how the economy plays in it. We all want to get into Fleets whizzing everywhere etc, but until you nail the economy and the early game, you'll never enjoy GalCiv.
If you get frustrated - honestly, we've all been there, however confident anyone may sound - dont give up, come onto the forum, post a screenshot of where you are at, and people will help you walk through a game if that's what's needed.
Anyone flaming a new player on this forum for asking basic questions dies a horrible Cyber-Death

, so dont hesitate to yell as time goes on.
Regards
Zy