Im not sure what weapons to be picking up.
Shotguns over SMGs as secondary? Do pistols even matter?
You should always try to balance range and damage per second.
My personal favorite combo is a fully kitted M4 and SKS. M4 has a high fire rate and is good for building clearing. SKS is good for ranged targets on the move and IMO is easier to get kills with because the second shot is easier/quicker to take vs the Kar98.
A more common scenario could be going with something like an M16 and an SMG. The M16 can work as your long range weapon and the SMG for everything else.
I always try to have at least 1 full auto gun. Something like an M16 and Kar98 is less than ideal in close quarters combat. Shotgun and Kar98 is just asking for trouble.
I would also factor in what stage of the game you are in. Early game, I love going for an SK12 because I can engage multiple people, likely with weak armor, easily. Late game, I would go a double barrel. Solo, I love the Vector w/extended, but in squads I will want the ammo capacity of an AR or UMP (extended mag).
In terms of pistols, the only two worth equipping are the G18c (w/extended mag) and the revolver (great w/suppressor). It helps if you can use an ammo type for a gun you already have. Otherwise, I don't usually bother with a pistol... maybe I carry 1-2 mags.