1. He became the shivan's new pet monkey, in essence. There's little reason to believe they'd simply kill him. Shivan's are certainly all too happy to kill Terrans for no apparent reason then they were there, but obviously this isn't the case with Bosch.
2. Because they understood the broadcasted message. Bosch's monologues suggest that there was at least a two way communication - and the fact that of the thousands of crew on the Iceni, the Shivans isolated Bosch and a few lieutenants - points that the Shivans managed to get enough info to figure out, at the very least, who was in charge. Humanity has been relatively successful in combating the shivans - and despite how absurb it may seem to us, the Shivans may have been interested in Bosch's offer of an alliance because they need the help. See 7.
3. From subspace. It's a big universe, and humanity isn't exactly on the forefront of hyper advanced subspace technology. They'll just show up from somewhere we didn't know about.
4. The shivans are a race from another dimension. They have no 'purpose', any more then Humanity of Vasudanity has a 'purpose'.
5. Yes. Though, if you're expecting anybody there to be a big help, you're probably vastly overestimating the amount of resources left on earth.
6. Excellent recycling technology and Alpha 1 the 1sts great-great-grandchildren.
7. The shivans didn't cause the actual explosion. Something else is causing stars to explode, primarily in areas which have seen large amount of subspace travel and high energy discharges. The shivans sole purpose there was the emination of the subspace field, which prevented Capella from taking the whole flippin universe with it. Including the shivans own home dimension.
They don't know what's causing it, but this isn't the first time the shivans have preserved the universe from a sun about to become something much less pleasant. Lacking a real cause, even after millenia of investigating, they do what they can - mitigate the explosions through subspace technology and destroy any uppity races statistically likely to cause more explosions through their trigger happy ways.
This problem is part of the reason why the Shivans were interested in Bosch and not his crew. Humanity has shown great adaptibility, and this particular human had shown great initiative and insight, and thus might help them finally figure out why the universe is breaking. By this point, they're probably happy to take whatever help they can get. Unfortunately, the majority of his crew were NTF, and thus fit the 'trigger happy idiots likely to break the universe even worse' mold, and paid the price.
8. Essential full integration within 30 years. While still distinctly different species, they are socially one organization - and instead of having racial tension, go back to the old standby of blowing each other up for purely political reasons.
Assuming all of this is wrong - and it probably is, my only other guess is:
1) Two words. Anal Probe.
