First
What are you buying a wig for?
This changes how forgiving the wig needs to be more than anything else you tell us.
Second
How often will you actually wear it?
Be honest here rather than optimistic — it decides how long the hair should be.
Third
If you could only have one of these, which?
Every wig trades something off. Pick the one you would not give up.
Last one
How do you like to wear your part?
This one decides the lace size — the single spec people most often get wrong.