nobody going to give my questions a go?

For the first question, min and max bounty threshold control (I believe) at what bounty the formula begins getting used. There is probably a minimum bounty threshold to prevent divide by 0 errors and strange math when dividing by large numbers. I have noticed that, sometimes, if a bounty is above 3000 specifically, the pirates will also attack that target at the next raid point, as they will attack more than one player. (At least, that sword icon comes up next to them when more than one player is above 3k bounty).

Second question: not sure if this is a question, really. If you want to change it, go right ahead.

3A: I think it's a part of their AI to retreat after a planet has been destroyed because the developers didn't want pirate raids to be the end-all, be-all of the tactics, especially on multiplayer. It's already a good advantage if you have pirates chasing the enemy while you stockpile your fleet. If the pirates would keep planet hopping until the full bounty was depleted, you may not ever have to leave the comfort of your gravity well to win the game.

3B: I am pretty sure it uses percentage of supply. At least, it does not appear to be a huge random range.

Fourth question: You may not want to double the strength of the supply. I'd try it at 300 and see what it does for you. If you double the supply, you might get tons and tons of very powerful ships that might ruin the gameplay.

Fifth: Yes, it controls the raid times. Whether it is the "imminent" time or not, I'm not sure, but increasing the times will increase the time between raids.