This is EXACTLY the place to be for this kind of question. Welcome abaord.
1 - As long as the 6 DP have been paid it doesn't really matter where the point come from. Early Life history is way OK, after all, if you dont know if you want a 'half-breed' by that point, then its probably too late...
However the DP's assigned are not linear, simply a numerical value of the characters make-p and experience over its life so far. So there is equally nothing wrong with paying for the Mixed Species during the characters tours... (either assigning the advantage early and paying it off ASAP, or through a bizarre transporter accident).
2 - Yes, in theory you get the edges assigned to that attribute. However some narrators here have suggested either;
a - building several 'stock' templates for the most common half-breeds
or
b - using the sum total of edges, so if there is a plus and minus... do the math and apply the result (upto +/- 2 maximums)
3 - The best way to think of this is to ask which culture the character grew up in?
Spock was a Vulcan/Human growing up on Vulcan (and so he viewed himself as Vulcan first, and would be assigned the Vulcan Skills and Advantages.
Belanna was a Human/Klingon, growing up on a human colony, and so she would have the human skills and advantages...
Does this help?
DanG/Darth Gurden
The Voice of Reason and Sith Lord
“Putting the FUNK! back into Dysfunctional!”
Coming soon. The USS Ganymede NCC-80107
"Ad astrae per scientia" (To the stars through knowledge)