How exactly do allies work?

From what I read here on the forum. The ally you use goes on cooldown for 4 hours. And the hero that is available is the leader of the team they last used.

From what I've seen today I'm pretty I've used the same hero from the same ally more than once in the last 4 hours.

I've noticed the more allies I get from my own server the more available it becomes. Just an observation I can not confirm

How do you know what server you're on and can you change servers?

When you fight someone in your arena for the first time it will give you an Allie request option.

I would also like some clarification on how the ally system works. I go to the cantina battles and I have plenty of quality hero options including my own allies, but when I do the dark side battles lately I have lousy options and none of my own allies show up. What gives? Are people really sending in one or two star characters level 47ish green gear with no leadership ability (stormtrooper, geonosian soldier) as their leader? Are these generic heroes that the game always makes available? Any info that anyone has would be greatly appreciated.