Bingo!!!!

Ship maintenance is the largest expense you during times of war. You need to develop a robust economy and a substantial warchest should you decide to go to war. I only played GalCiv 2 twice (currently on 2nd game) my advice is as follows:

1. Dump your imperial economy ASAP. Starting with a Republic you get a 10% bonus to your economy. A Democracy will give you +20%. The Federation will give you +30%.

2. Research technologies that allows you to build better factories and economic centers.

3. Populate as many PQ10 planets or higher. Never place more than one 2 farms on a planet for a population cap of 18 billion people. The next stop is 24 billion people with a 3rd farm you will need too many enterment structures to keep your approval above 70%.

EDIT: Build two of the most advanced farms you can research on non-bonus tiles will give you a max population cap of 20B people. Three will boost that to 27B, you don't want that many people.

4. If someone proposes that every race switch over to a Star Federation type government, vote yes.

5. While it may be good to have planets devoted to manufacturing or economics, I think it's best for most of your planets to be a combination of the two so that you can see how well each planet is doing in your Colony Screen View. Don't forget to throw in a Science lab or two either.

6. If the random event "Economic Boon" happens then take advantage of that to quickly build structures and save money as well. You can dramatically increase your treasury during this time.

7. If you can keep a minimal fleet of ships then do so. That way your fleet will not sap too much of your weekly income. I go down the "defenseless" route. I absolutely have no armed ship. The closest thing to any type of warship I have is the default flagship and a couple of unarmed scouts. It is the year 2230 (5th year) in my current game on the "challenging level" (above normal) and I still have no armed fleet whatsoever.

8. When designing your ships, be aware of the maintenance cost. That can quickly drain away your income. Even though economy is very robust and I have a huge warchest, I try keep the design of each planetary defensive ship to no more than 30 credits per week. I also try to design capital ships with no more than 100 credit maintenance. Note, I said design. I haven't built anything yet. Soon though, very soon.

9. Look at your empire expenses every now and then adjust your taxes accordingly to maintain income every week. Don't set it too high or your approval rating will drop. I currently have my hax rate at 43%.

10. Forgot to mention this before. Set the galaxy to huge. The more planets, the more income. But the game can take longer to finish. That's the way I like it.

11. Don't forget trade income either. If you trade with a race they are less likely to attack you.
I'm sure I'll pick up some more nuiances about the game as I play it more.

Pretty much. Unused production (on planets that are not building ships OR improvements) gets refunded, which can give you a false sense of economic security that is shattered once you go into wartime production mode.

Ideally, you should have way more than enough troops & transports to conquer the planet, and also seed it with a respectable population (~3 billion). War-time is usually not ideal, though. But if you can, you get to reuse the transports you used to ferry that extra population. When I play, if I'm in control of things, I spend a little extra time building a few extra transports, and also during that time research the soldiering techs. Neglecting the soldiering techs is a great way to wreck your war economy, too.

Another trick is you can espionage the planet's farms and morale structures and then info warfare it. When you take the planet, you get the agents back. Costs 800bc, though (unless you're evil and have the No Mercy Invasion Center, but that thing isn't worth it except on very large maps).

I've never upgraded a loaded transport before, but it sounds like an interesting idea if you've got vast swaths of space you're crossing. I've always just invaded with the old ones and built new ones to replace them.

What I have done before, though, is trade with the AI for his transports and he sold them to me loaded. SWEET!!!

Are you secretly a spy for the Korath? Thou must die!! Evil evil! We must enslave the colonies, not kill them all!

My idea is simple: wars shouldnt last much.

Dont get into wars easily. Sun Tsu said it 2500 years ago. Wars cost a lot, both to your economy and to your population. If it drags too much, you will lose as much as the enemy.

That means you have to win with as much strengh as you can, and quickly. Build a lot of strengh close to the borders, and when you think you´re ready, strike the enemy capital. Its all about the planets. Ships are useless. What you need is to take care of the planets, and make sure people dont invade yours too. You can win entire wars in less than 6 months.

If people atack you, let them come to you. They will be the ones who lose time and effort.

My experience has often been the opposite. I'll let wars drag on the entire game. This isn't Civ4; there is no war weariness. It's a little inconvenient to have to watch my back all the time, but hey--let him spin his wheels cranking out starships for me to turkey shoot. That's better than him pulling ahead in research. It would be nice if I could just invade all his planets and end it, but I have other priorities.