As for your last question the reason for doing missions for Wangal Energy Partners was that in order to start a civil war their influence needed to have parity with AIE. The original mission was to start a civil war and take over all the stations in Wangal. However that proved to be difficult with only one system as an operating base, so it was decided to expand into other systems by raising AIE influence in Wangal to 80%+. Then with a second area the bulk of AIE could work on expanding into another system while a smaller group could work within Wangal to start a civil war. It seems the plan is to have most players expanding into new systems to raise the sphere of influence whilst a smaller team works behind them towards the acquisition of the rest of the stations in each system.
You will not see missions for AIE that I can see in any stations outside of Wangal, however they are available at all stations within Wangal.
I did some Nav point hunting last night and depending on you combat rating I think I cleared 1.5 mil in bounties in about 2 hrs +/- so it seems viable to me. When they refer to bounty hunting they mean to turn in your bounties at docks we own i.e. Nelder City. The faction you turn your bounties into is the one that receives the influence bonus and it increases your relationship with them. Any ship is fair game that is not AIE do not shoot AIE ships even if they are wanted!
In regards to trading as long as Nelder City is in your loop your good to go, I found they generally have a Medium supply of imperial slaves which you can sell anywhere with high demand for a decent profit.