D.W.
The BEST way to increase your supply is to have your baby nurse most often. Nothing else stimulates breast milk production as well. Yes, you can pump more often, and it will likely help your production, but the best way is always to have your child nurse.
People will recommend Fenugreek. I never tried it personally, I preferred to use the above mentioned ways when needed. I was lucky to product a LOT more than I ever needed for my kids.
I am sure it's fine to wear push-ups - I really think it's all about your personal comfort. I, personally, liked to wear athletic bras because I HATED nursing bras. I think it's a matter of personal preference. I don't know of any reason not to wear what you prefer, but you may want to ask your OB/GYN for a medical point of reference.
Good luck! It's a great thing you're doing.