Can something like a cam droid integrate gear?

How much?

GM's call. Encumbrance and common sense should be the guide.

One of the Drawbacks to this system is while there are rules for buying and constructing NPC Droids, there are none for simple Modifcations/Upgrades.

Theoretically you can buy Cybernetic Upgrades for Droids to act as "Modifications" but its not quite the same. At least PC Droids can, but I see no logical reason why you can't do the same for NPC Droids but likely up to the GM to make that call.