if you are alredy on MG2, you should have a working kernel for the minimalzero rom. alternatively you can use D-kernel.
as for the firmware itself, it's like an os. the package is a full rom (system installation, so installing it will first wipe your current system and then recreate it from scratch.
stuff like wifi passes and mms are on data tho, so u will keep that
for aosp based roms tho, the kernel needed will be included in the package, and a data wipe is required as well.
Flashing anything should be done by first flashing a temporary CWM via the stock recovery (look for temporary CWM by shaan in the development section) and then flashing zips from the temporary cwm once itl oads.