since im new to the whole audi stuff please be easy..... i was tired of all my hondas and acuras...still love them though..

how do i go about refilling the ac..... i have a 96 A4... there is no fillup valve...

what headunits can i use if my car comes equiped with a bose system.... is it an easy install??
the reason for it is that i would like to have a cd player... i hate changers..... an info or advice would be greatfully appreciated.....