Retin-a / Tretinoin Strength for Getting Rid of Sebaceous Filaments on Nose & Closed Comedones on Fairly Dry Skin?

I have large,clogged pores on my nose and on either side of my nose that I haven't been able to get rid of (or at least diminish some) since age 13 (now 25) and the awful, tiny closed comedones on my forehead that never grow and pop, and never go away. My skin is a little sensitive and kind of dry. I'm a little afraid .25 won't be strong enough and that .5 will be far to strong. My dermatologist said, "I can give you retin-a" but didn't go any detail about strengths. Any advice is great. Thanks