It's hard to find objective information, as the pros and antis have competed to yell the loudest. This is a pretty good overview of some of the issues:
Keystone XL Pipeline | StateImpact Texas
I have some of the same questions you do. As to eminent domain, the states it is running through apparently are letting corporations condemn and seize private land for the use of the pipeline company. In my view that is a horrifying prospect, but it isn't new.
There has been a lot politicing over this, but not a lot of objective educating of the public.