A question on filter order and gain
Any gain that you get in a filter is incidental to its operation. A passive LC filter will have nearly unity gain, a single Sallen Key filter stage will have gain somewhere between 1 and 3 depending on how you configure it. 

Design your filter, find out what gain it has, and make up the balance with an amplifier. Noise and signal level issues will determine whether you put the amplifier before or after, or even split it before and after.

You can add capacitors to amplifiers to shape the gain, but anything more than single order sections quickly becomes 'design the filter, and design the gain'.