1: 90 to 100 range is the standard, any where in that range is good but the closer you get to 98 is the best. If its a little low rub your thumb against your clothes for a couple seconds then hold it against the temp strip on the collection cup for a couple seconds. When it says 98 walk out of the room.

2:False negatives can be a problem. If it hits on the blood pressure medication its not too big of deal. They'll send it to GC/MS for confirmation and show that its not one of the regulated substances and you'll be fine.
I have never heard of birth control pills hitting a false negative but if it did it coulld be a problem if you're a male.

3:Sould just be the standard drug test.

Synthetic is still the better option if you can come up with some.