Here is what I would do: find out who the strongest race is, and bribe them into declaring war on as many races as possible. That should keep them busy until you are ready. With a bit of luck, that will wear them down enough for you to easily crush them.
If one of the other races asks for help, provide it to them (some low-tech ships will be good enough). You can make good friends this way. Also, position some constructors around the enemy's resource starbases. Once they get destroyed, you can easily take the resources over.
also, my loyalty was at 80%, so i lowered my my taxes so i was at 100%
I think you mean approval. Loyalty is neither ranked, nor is it affected by taxes.
Anyhow, there are three things, that negatively affect approval: taxes, being in debt for a long time, and high population. The last one is what you are seeing (and one of the biggest problems in keeping the people happy). The higher the population on a planet, the lower the approval and all bonuses to it (only the bonus for high quality planets is unaffected). If you mouse-over the approval rating in the Colony Management screen, you will get a tooltip that shows how the value is calculated.
A good max population is 14b. The approval penalty isn't too high, making it is easy enough to keep the people happy. For your economy planets, consider a population of 20b. It requires a bit more effort to keep so many people happy (i.e., more morale improvements), but the increase in tax income should more than offset this. Never go above 20b though, or you will pay an arm and a leg to keep your people happy (and still most likely fail).