Generally... :
the A models were fighter versions
the F model was a ground attack optimized plane with additional armor, it replaced the Ju 87 Stuka in the CAS role.
the G model was a long range fighter bomber, it had provisions for droptanks on the wings and was mainly used for raids on the channel coast etc.
the ER 4 rack was often used by the F models.
the big confusion thing is that many of the "modification kits" were used on normal A version planes early on, before the dedicated F and G models went into full production.
Virtual any version could pack a single 250 or 500 kg bomb on the centerline rack for ad-hoc fighter-bomber missions.
For internal cannons of the F and G :
all F had the 2x 20mm MG 151/20 in the wing roots and 2x MG 17 (early) or 2x MG 131 (late)
all G had only the 2x 20mm MG 151/20 in the wing roots .
Wrench, in case you need any info on 190's, I have dozen of books about them, just yell