Does perceived ADC resolution, range and precision depend on fixed point format? What is the best way to deal with this for signal processing?
it may turn out to be very inconvenient, but you can do essentially anything in fixed-point that you can do in floating.  as long as you got "Add-with-carry" as an instruction and enough MIPS to do all of the multiword instructions you may need.  the 12 bits that come from your ADC don't care if it's fixed or floating and your ADC resolution is the same regardless.  can't promise that the quality of code coming out of a C compiler will be any good.