[Alpha Kodiak]

You touched on the most important consideration: have a plan for what the race will be like before you start. Once you do that, getting the politics and anger settings can be sped up by looking at a race or races that are similar in character to the race you want to create.

From a research perspective, decide whether your race will be aggressive militarily, thus researching mostly combat techs early, or whether you want them to spend more time on infrastructure research early. If you make them research combat techs early, they will be nastier to meet early on, but may slow down as the game progresses as they try to catch up on research/production technologies. On the other hand, a race that spends too much time researching infrastructure early will get killed if they run into an aggressive opponent early.

The one thing that I can say definitively is to make sure that your race builds plenty of colonizers in all AI states so that it can keep expanding as long as there are planets to colonize.

The thing I did to start was look at some of the custom races that I liked to see how they were doing things. Then I read the forum to see what everyone said made the AI weak. I came up with a plan to minimize the weaknesses that were listed. That plan evolved into the Rage Collective. Since then I have tried different ideas for AI's, but always try to start with a plan.