Tech priority is very simple:
1. Two engine techs first on larger maps. On smaller maps you can skip the second one (but you still want the first engine tech).
2. Hives and Hyperion Matrix if you're the Thalan.
3. Interstellar Government line for raw production boosts.
4. Whatever it is that you lack.
In other words, to make a rule set for the AI YOU NEED TO BALANCE THE GAME MECHANICS FIRST.
For example, if I'm playing with the old LEP system of -0.2 morale/planet, I'd focus on getting Supportize Population early for +4 morale. With Nassie's -0.2 Money/Planet, getting things that boost income and population (such as Planetary Adaptation) becomes a lot more important.
Also, Naselus changed colonial hospitals to provide +0.1 growth instead of +10% growth (which most of the time does nothing), thereby making planetary adaptation an important priority in the early game. In the base game itself, Planetary Adaptation is much less important.
Which LEP system are you planning to use? What changes to the game mechanics are you planning to make? Because the moment you make a change, I automatically know what the best strategy will be to take advantage of it.
In the base game, Thalan tech is the best. Hands down. Don't even bother talking to me about the other cruddy tech trees.
To make a "good" AI in the base game you should just give every AI Thalan Tech, get them to expand in the early game, and teach them to build Hives as the first building on every colony, and get Gaia Vortex and Hyperion Matrix ASAP.
For economic expansion, you want a mix between expanding raw production through things like the Interstellar Government tech line, and expanding %manufacturing or %research (money is worthless in the base game). Consider:
+50% raw production, with +50% manufacturing = +225% production. ((1+0.5) * .5 = 2.25)
+100% raw production with +0% manufacturing = +100% production.
+100% manufacturing with +0% raw production = +100% production.
Things that increase raw production are economic rings and interstellar government techs. Things that increase %manufacturing are things like factories and Starbase Factories.
IT'S MUCH EASIER TO INCREASE %MANUFACTURING THAN IT IS TO INCREASE RAW PRODUCTION. CONSEQUENTLY I PLACE AN EMPHASIS ON INCREASING RAW PRODUCTION SO THAT I CAN TAKE FURTHER ADVANTAGE OF THE MANUFACTURING MULTIPLIERS ON MY PLANETS. THIS IS ALSO WHY HIVES IS SO AMAZING BECAUSE IT DRAMATICALLY INCREASE RAW PRODUCTION. IF YOU DO NOT UNDERSTAND THIS YOU ARE NOT SMART AT MATH.
As a math tutor, I have a question for you: under this scenario, what is the OPTIMAL balance if you're limited to the constraint of Raw Production + manufacturing = 100? PROVE IT WITH CALCULUS.
DOING ANYTHING ELSE IS LITERALLY INCOMPETENT COMPARED TO THE STRATEGY OUTLINED ABOVE. IF YOU DO NOT BALANCE THE GAME MECHANICS, I WILL CRUSH YOUR AI LIKE A HAMMER ON TOFU. MAKING TOUGHER TOFU (WHICH IS WHAT YOU'RE TRYING TO DO) ISN'T GOING TO HELP AGAINST A MEAN, ANGRY PERSON WITH A VERY LARGE HAMMER.
In other words, you might want to consider changing the game mechanics to the fit the AI than the other way around. Much easier that way.