In the MOO games, a colony ship took a long, long time to build. But in Space Empires IV, they are essentially free. When you start the game, you would do well to build a space station with a space yard as the first thing you build. Then, start cranking out tons and tons of colony ships. You should be building colony ships throughout the game. If you don't have at least one being built and another on its way to colonize some planet, then you aren't expanding fast enough.
I am a fighter fanatic. Fighters are great because you don't pay maintenance on them. They are great for both offense and defense. In the early game, they are killer against races that build ships with just missiles. Later in the game, you can have an effective military that is easily twice the power of every other empire combined but NOT trigger MEE because units are not included in the score calculation. This makes fighters an extremely worthwhile investment.
When you consider which enemy to attack first, look at their race properties and figure out what atmosphere they breathe. If your race's homeworld is rock and oxygen, then you can only colonize rock worlds and only get the full number of facilities if the planet has an oxygen atmosphere. This means that if you find a huge world with 150% minerals that has a Carbon Dioxide atmosphere, you are NOT going to be able to build the full 25 mineral miners. Instead, you have a domed colony and only get 5 mineral miners.
But let's say that a nearby enemy AI breathes Carbon Dioxide. Then, you would do well to capture one of his planets with troops and transplant those CO2 breathers to your huge CO2 world. When you take the Last one of your Oxygen breathers off the colony, it is no longer domed. Voila! You now get to use all 25 of those facility slots on the planet.
Oh, another thing about fighters: you can build them on any planet. You can build them on all planets. Hopefully, you will always have a surplus of minerals. Don't build a storage facility. Instead, tell several of your planets close to the front lines to build fighters.
If you expand fast enough to grab enough systems before the other empires colonize them, then I think a good plan is to turnaround when you see a juicy planet in a system that already has colonized planets from another empire. It seems like colonizing a planet in a system already claimed by another empire is a sure way to get them to declare war on you early.
There is a big difference between Space Empires IV and MOO because of the wormholes. In MOO, you pretty much had to establish defences on all your planets. But in SEIV, you can and should try to establish chokepoints where your focus all your forces. Ideally, you want to keep those down to as few as possible.
BTW, have you downloaded the TDM ModPack and TampaGamer's Sounds yet? I wouldn't play the game without them.