There are a lot of different strategies for this, and you should give them all a fair shake. What you're doing isn't wrong by any stretch of the imagination though.

A few points:
1) You are absolutely correctn in loading up the colony ships as far as they can go. You have 8000 people on your home planet (or, at least, you do in Dark Avatar), so it's not much of a dent in their population, and it'll mean your colonies will populate FAR faster. More people means more taxes.
2) Buying colony ships is expensive, as they cost more than a thousand BC to quick buy. With 5000 BC in starting cash, that means you can only do that for one or two colonies. You'll have to find the right balance between how much of the BC you're willing to spend versus how fast you want to expand. Also, keep in mind that building a ship part way and then quick buying saves you a fair bit of cash.
3) If you can build a decent industrial base fast enough, then you can build colony ships fast enough that quick buying would be insane.
4) A strategy to consider: simply quick buy an improvement on your homeworld each turn and keep social spending at 0... your plant will develop without having to divert resources from ship production.

Yea it can be very dangerous (as i have found out ><.) If you use the strategy to colony rush, i found it helps a bit to get your civs points into population growth so you hit +70. The problem i have run into with that is morale. Its tough to keep the morale up with such a high rate of growth. Granted, putting Multimedia Centers helps, but it can be more or less of a quick fix as the planet gets larger. I have also tried buying factories on my planets instead of colony rushing, but you have to be careful because this will also make your maintenence costs rise to an amount thats hard to keep control of in the early game. Im trying to find the middle point of the two strategies to see if that will do anything, but thats my input on the question, dunno is it will help though   

I don't get that industrial capital strategy? The colony rush is over before you get the tech??

One tactic not mentioned here is to decoy AI colony ships....

When i beat the AI to a planet with my colony ship, i do not colonise it! Instead i wait for the AI colony ship to aproach and then colonise it in front of him!! That way he has to make up allot more turns to reach the next vacant planet. The AI is a real sucker for this trick

Depends on the map size and number of habitable planets IMO. If planets are *very* limited (ie less than half a dozen per race) then you probably can't afford to wait and rush buying is a good idea. Otherwise, I wouldn't recommend it. I'd go further and say as a general rule of thumb, rush buying is a very inefficient use of BC and should be avoided (but in such a complex game it's easy to come up with specific situations where that rule doesn't apply!)

I buy factories. Here's what I do if there are no production bonuses on my homeworld. (This is a DL strat, I haven't played DA yet)

Turn 1. Buy a basic factory (438bc) on your homeworld. Focus on Military production. Set spending to 100%. Set Social and Research to 0%. This should get you a colony ship in 3 turns. (At least with the custom race I'm playing)

Turn 2. Buy another basic factory on your homeworld. Lock Social at 0%. You can now adjust the military down from 100%, but making sure the colony ship still builds in 2 turns. This gives bit of spending to research.

Turn 3. Buy a third basic factory on your homeworld. Once again adjust Miltary to just enough to build the colony ship in 1 turn. This gives even more to Research.

Turn 4. Out pops your colony ship. Buy a fourth basic factory on your homeworld. Adjust the Military slider back up so your 2nd colony ship will complete in 2 turns.

Turn 5. Buy a fifth and last basic factory on your homeworld. Adjust the Military slider down just enough to build the colony ship in 1 turn. I think it ends up something like 90% Military, 0% Social, 10% Reseach.

From here on in you will be pumping out colony ship every 2 turns.

Caveats:

If there is a production bonus on your homeworld you can reduce the number of factories you buy. I usually buy 5 anyways, just to get the higher research via being able to bump the Military slider down lower than if you had no bonuses.

When colonizing a new planet during this phase, you must set the new planet's focus to Social or nothing will get built. My build order is usually 1 basic factory then 4 markets, unless there is a research or production bonus. If a research bonus, I build 1 basic factory and the basic research building. If a production bonus I buy 1 basic factory and build a starport to begin building constructors.

After the colonly rush adjust the sliders to a more balanced setting.

On Edit: Double post. Sorry.

I don't use scouts - don't have time. My colony ships do my exploration.

I may take a pause in the colony rush to build a few cargo survey hulls (after I get Sensor 1), though. They serve to see the galaxy and grab anomolies. Later they make great sentinals to make sure Bad Guys aren't sneaking in.

Hydro

When your scout finds a planet, you get to see what a nice planet the AI is going to have!

better to have a colony ship to explore, there is no need to colonise the first planet it finds... keep exploring, and then when you find a nice planet that seems likely to be claimed by the AI, you can do somthing about it, unlike if you used a useless scout to explore.

If your playing as terran then the best way to find planets is with colony ships. Since the technology for sensors is a bit too much of a stretch away to be of any use during the colony rush.

You can trade for Stellar Cartography and research Sensors directly. That's still not terribly expensive.

with my custom race the poth'Ead, in the first turn, i buy a factory on my home world and a scout, send out the scout and survey ship(in different directions) to get anomolies/explore (when hes surveying, hes exploring in a way) and colonize the class 4 planet in my system and only buy and que factories and a research building (no starport (depending on the # of upgradable tiles i might get one later)).

in the second turn i buy a second factory for both planets and a second scout and send them out

third turn i buy one colony and start finding habitable planets.

from the beginning i set taxes to 35 and ramp up military to %60-80 and research to %30-40. with this opening and my survey ship immediately collecting stuff, i usually do ok but i dont get my economy as stable as i would like until later in the game and i end up lagging slightly behind the other races. with diplimacy i go thru and trade for all the techs i need with races that have an equal or less dip. skill.

i only play on huge galaxies and usually have tech at very fast.
any advice about how i could get my economy up faster would be nice, but i think its just a tweaking of the sliders that may be my problem

I have been building cargo hulls and upgrading them to engines. If a plan my civ carefully I start with up to 4 ion engines going at 7. When I find a good planet I upgrade to a stripped down colony ship and colonize with 1 pop. On a small map I need 2 basic life support to reach everything, so I design a colony ship and scout, both with 2 basic life support. I also design a colony ship with ion engines for ferrying pop to my colonys. This strategy allows me to save my home world for growth, which ends up making more money than I spend. I am doing well initially with the rush on AI intelligent, however, I am struggling with the tech tree choices - either I go for the extreme colonization to prevent the AI from getting some really good PQ 15 - 20 worlds, in which case I fall behind militarily and get attacked, or I focus on my military and get squeezed to death by the AI influence, especially when UP proposals start making me pay rent. I need a better grasp of the new techs and what they do. After my colonies have 1B+ pop, I will que up a factory, farm, eco building, star port, and research building - usually in that order. By the time they finish building I'm in the green the whole way. My fast hull strategy allows me to get most of the resources in the beginning. I find though, that there is a delicate balance between when to upgrade a hull and when to build a colony ship or constructor. I put my survey ship on autosurvey and forget about it. I did try some advice on civ graveyards, but no matter what I did they never changed - reload, etc. They seem to have bonuses that are generated during map creation, not exploration.