Shame on me (or help me!!!)

[Will]

I will suggest this: don't attempt full-scale attacks, it isn't needed!

Your first general priority is to secure what you have; pile mines on warp points, have defense fleets ready, have more mines/minelayers ready. Like SJ suggested, be sure to utilize empty systems, the more supplies enemies use to get to you, the fewer they have to hit you with.

After you are fairly secure, create raiding fleets, as this would seem to fit your strategy perfectly. Use your 3:1 fleets, and throw in a few boarding parties to bring back technology/ships. These will work best if you create a small base for the areas your raiders will be working in. A moon will work fine, keep a resupply depot on the planet, and have a SYS stationed there, or build a BSY with it. If you get 3 or 4 of these going, you should do fairly well, and since they would be fairly easy to replace (just have a few mothballed raid fleets with a colonizer and SYS included, or if you're like me and look on mothballing as an unfair human advantage, keep one such fleet in reserve).

While in the "raiding" phase, develop infrastructure and research Troops and Stellar Harnessing. Once you have max tech for troops, your frail little insects can be pilots of high-tech battle tanks, and your vastly stronger foes will wither before you The design I use is LgTroop,1xCockpit,1xShield,5xLightningRay. Build up a good number of these troops, 500 should be good. Then build a Medium Transport that is protected for battle; either lots of OA, or my method, a Stealth Armor and shields. Also build a "Supply Transport" or two, just a medium-sized hull (LC-BC) filled with the essentials, a few supply storages, and the rest Solar Panels. You can do the math of the most efficient ratio of storage/panels for your fleets, keeping in mind that only the supplies that can fit in the supply ship itself will be generated for the rest of the fleet. Put the transport and supply ships in a fleet with two Raiders, then send them to attack the enemy (it is also a VERY good idea to send a minesweeper and repair ship...). It is suprising what a small, ~10-15 ship fleet can accomplish . If you use strategic, be sure to set your fleet strategy on one that captures rather than glasses a planet. I posted mine somewhere... Once you capture one planet, turn it into a base; build a BSY, build a resupply depot, launch a few defensive mines, build replacement troops, and defensive ships. Proceed to take every planet in the system, and fortify it like one of your own (be sure to keep some troops on all captured planets to prevent rioting). Once the system is secured, you can begin rebuilding the planets to fit your purposes, and using this one captured system to spawn a few more Invader fleets, ones that won't need the supply ships, since you're right on your enemy's borders.

Then, by the time you have conquered a few AIs with the Raider/Invader attack, you will be closer to full tech, and have the size to send all-out assult fleets (think one Invader fleet for every planet in enemy system, and take all at once) to the remaining enemies. From this point, it can get boring sometimes, as the AI will be no challenge

After you get a few "practice" games in with this strategy at your current settings, start making things more difficult. Things you can do are make a smaller quadrant, more difficult AI, higher bonus, no neutrals, custom AIs. Then the really fun ones, which can either be enforced for everyone, or just for you (a lot harder if it's just you): Colonize Only Home World Type and Colonize Only Breathable Atmosphere. Also be sure to take all the precautions you would take with a human opponent, to prepare for something like PBW. Humans keep going after one layer of systems is captured/destroyed, while there have been few reports of AIs going further. Humans will constantly redesign their ships to match yours.

Hope that helps