Solution to the 5 gadget need.

[Tidenburg]

Imagine a sticky camera, but bigger and with an empty space where the lense would be.
So basically in your inventory selection screen you can choose your standard four gadgets plus one
you get four of this gadget (smoke, gas, chaff grenades, 2 tazes, etc) this last gadget is automatically placed into the launcher which can be fired from your gun (has more of an arc like a grenade) you have 4 launchers and each has one of the gadget you selected in it. You can then access these at any time (but only have one on the map at the time)
The launcher doesn't count as a gadget, only the extra you select does and cannot be changed during gameplay.

[Farley4Fan]

I say with 5 gadget slots you should get three or four of them each.  No amount of five of any gadget should be in this game since you already have four other gadgets anyways.

[Cyntrox]

That's an interesting idea... I'm all for trying it, but it would need gameplay testing.