A lot has already been said, so I'll try to be concise here.
2. Meals and beverages are not a consideration for me when I take my pm dosage.  I'm not aware of anyone reporting of this making a difference.
3. No, I don't think 12 hours is too far apart between doses.  For a decent portion of my pm regime, I took my pm capsules twice a day and that didn't seem to impair development.  If you're having trouble with development, it's certainly worthwhile I think to keep a steady supply of pm in your body to see if that helps make a difference.  
4.  I take 800 mg of spearmint and that's enough to make a difference for me.  As CK mentioned, you may need to give it more time.  
5.  Did you buy a different brand of PABA from Swanson?  The ones I got are 500 mg per capsule.