I have been trying to design a simple unit with the pro-mini from e-bay. there are multiple chip layouts. some of A6 and A7 on the end next too A4 and A5, others have A4 and A5 nestled inside next to A3.....
also, because of the way A6 and A7, and A4 and A5 are laid out, you cannot use a common breadboard.
the price you pay for not paying a high price.
another option here might be the Teensy. it has on-board ADC, 13bit usable. (16bit ADC)