Its kind of a balance. If you colonize too many planets too quickly you might kill your economy but once the population of those planets increases to a high enough level they should be able to pay for themselves. However a factory or lab planet will always be spending more than you can get from it in taxes. Thats why you need to have economy planets to support them.

The above is decent advice but one thing to point out is that early on its often better to decrease taxes rather than increase them.

Your income is proportional to the square root of your population. If you can lower your taxes to keep approval on your new colonies at 100% then you get the benefit of double population growth. The faster your population grows the sooner your planets become popular.

There are four different levels of approval that it's desirable to keep on your planets. 100% approval gives double population growth and can really help your colonies become profitable sooner. At 75% to 99% you get a 25% pop growth bonus but in my opinion this isn't worth the income loss. Between 41% and 74% your pop grows at the default rate. At 21% to 40% your pop doesn't grow and at 20% and below you lose pop.

There are really only two ideal places for a planets approval. 100% or 41%. If I can't keep approval at 100% then I just increase my taxes until my approval is at 41%. You will have variation from planet to planet and you need to keep in mind that its the approval of the particular planet that's important *not* the average approval so you may need to keep your average approval at something like 49% to keep all planets above 41%.

Anyway keeping taxes low early to build up your pop faster is counterintuitive but can be effective. Also you can't keep this up forever. You fund this behavior off of deficit spending from your initial 5,000bc. That's why it's important to never buy buildings except perhaps the first factory on your home planet. You need to save your cash to last as long as you can before eventually having to raise your taxes.

I'm also a fan of not building anything on your colonies early. If you feel obligated to build something let the planet build a marketplace. It increases the planets eventual income and doesn't add any maintenance cost to the planet. As you pointed out that initial colony support of 12bc is a killer.

Also try taking the pop growth racial ability, it can be a big help in getting your planets profitable.

There are many ways to go and a lot of this depends on the size of galaxy that you're playing as well as how well your economy is doing.

Growth in all resource utilization games (this certainly includes the Civ series) is exponentional. The more resources you have, the faster you grow. Once your planets start to become productive you use more and more of your economy to build up your newer planets. However a rule of thumb I use is about 2B. Once you're at this level the planet can usually start producing on it's own without going into the red.

Not sure what you mean by 5-7 in each category. As to what classifies as a good production it all depends on what you're trying to do. The beauty of this game is that there are so many different strategies and variations. I assume you've seen discussions about "all factory", "all lab" or "all economy" strategies. If not search around there's a lot of discussion about these.

Everything comes into play. Being evil and getting the Artifical Slave Center gives a hard coded 50% bonus to all military production. The ASC actually unique in that it multiplies all other production bonuses as opposed to "stacking" i.e. is additive. This is a big part of any factory focused strategy.

If you have a strong enough economy you don't need any production at all and simply buy all your ships. It's just so hard to give a definite answer, it really all depends on what you're trying to do.

For example one way to gain advantage over the AI is to outcolonize them. More planets means more people, more income, more production and more research. However you can also intentionally allow the AI to outcolonize you but make sure that the planets that you do colonize are top quality and invest more time and effort into making sure your planets are fully developed by the end of the colony rush. Then you can simply over-run the AI with their far more numerous but far less developed planets. I call this the the quality over quantity method. However both methods work well but just focus on different things. With fewer high quality planets you look to take over the AI while he's weak and before he can develop his planets. If instead you out colonize them then it's the other way around. You try to survive until you can develop all of your planets and then once developed you can begin to assert control.

For every way someone says is the best way to do things, there's a knack that you need to develop in order to make it work. On the other hand for almost every way someone says is not the way to go there is a way to make it work. The devil is in the details. It's easy to give some high level overview of some method of play but when you try to make it work you find it's far more difficult than it was described. The best thing is to play and try new things and then ask questions and try again. You'll find that some advice will help and some won't. But even when the advice doesn't help at first it's often good to go back later and try something that didn't work for you. You can find that something that didn't work for you before now suddenly will work and it's not because the advice was bad and is now suddenly good but it's because your experience and ability have grown and changed and suddenly now you "get it".