oki doki
with straight 2k colour providing you mix each batch precisely and lay enough paint to fully cover the panel then you wont get any colour variance painting panels seperatly (unless its along time between painting days).
if your car has been outside or damp alot since you primed the guards then id sand most of it off and slap one more coat on just to help stop any moisture blisters later on
as for gun look for a second hand sata or devilbiss even a well used one sprays better than a random Chinese brand, infact i could probably prise one from a painter at work, i use my gti pro for base clear and 2k and have 2 aircaps for extra wank factor between 1k and 2k paints but its not necessary