Half-Elf, paragon surge: Can I cast paragon surge multiple times in a day to gain different benefits?
No. The first time each day that you cast paragon surge, you must select a feat and make all the associated choices that come with it. Once that choice is made, it is set for the day and additional castings must make the exact same decisions.
Halfling, Warslinger: What kind of slings does the this reload ability work with?
The warslinger ability says, "Halflings with this racial trait can reload a sling as a free action." It doesn't say "any type of sling" or "all slings," just "a sling." The ability only affects standard slings, not halfling sling staffs or any other kind of sling.
Human: Where is the pure strain spell for the imperious bloodline sorcerer?
The pure strain spell was cut in development but its name in the bonus spells list wasn't changed. Replace pure strain with repulsion.
This has been noted for a future reprint of the [i]Advanced Race Guide[/i].
Celestial Servant: Does this change my companion creature's HD, saves, skill ranks for changing its creature type?
No. All it does is change the creature's type to "magical beast" (which makes it immune to abilities from other creatures which only affect animals) and give it the abilities of the celestial creature simple template (which does not change anything other than what is exactly specified in the template).