Silly question, does the Space Rig count as a "character"? Or is it strictly a vehicle?

Vehicles are characters as far as I know...

Nice, so it counts towards one of the four characters required for 6 pack recruitment?

Bridges newest recruit Mr. Mxyzptlk evil shenigans

Ok, quick question. From the wording of "exactly" 4 other characters sharing a keyword with Bridge, does this mean that the size of your force is limited to just 6 characters in total ?

Yes, exactly 4 + Bridge + recruited character = 6 (the trait is called Six Pack Recruiting after all).
The S.H.I.E.L.D. kw offers some low cost options, as does the Soldier kw (even for DC/Marvel cross-overs).
My latest "Six Pack"

Force Build 8795578 0
Set	#	Name	Team	Pts	Value
DP	041	G.W. Bridge		68	$0.79
SFSM	005	Thug		10	SELL
SFSM	005	Thug		10	SELL
SFSM	005	Thug		10	SELL
WK	WK-006	Toy Soldier		60	SELL
JW	059	The Joker		140	SELL
Force Total:				298	$0.79

So the Thugs choose Toy Soldier and G.W. Bridge to copy the Soldier kw; thus Joker becomes a Soldier himself. Thugs can be Mastermind fodder, but if you don' want to give points away, you can use Wooden Soldiers for that purpose. Toy Soldier can either copy BE TA to increase his attack or S.H.I.E.L.D. TA to allow Joker to get +2 to range (and even +2 to Damage under the right circumstances).

The wording on THUG says a Named Keyword. Soldier is a generic keyword so this wouldn't work.

Darn... that's a real shame... I guess this one might work then...

Force Build 8795637 0
Set	#	Name	Team	Pts	Value
DP	041	G.W. Bridge		68	$0.79
NFAOS	030A	Hydra Field Agent		25	SELL
NFAOS	030A	Hydra Field Agent		25	SELL
NFAOS	014A	Hydra Recruit		20	SELL
NFAOS	014A	Hydra Recruit		20	SELL
JW	059	The Joker		140	SELL
Force Total:				298	$0.79

You get 2 medics and some Hydra TA so Joker can get +2 damage from RCE...

Get ready for "Hit-Monkey, Agent of B.A.N.A.N.A."

Are we sure it was ever ruled G.W. could only be on 6-man teams? The wording sounds more like: You've built a force of 'X' [where 'X' is 6 or more]. 5 of 'X' have 'Soldier', so 1 of the rest of 'X' can have 'Soldier' as long as X-5= 0 Soldiers. So theoretically any piece under 125pts could be in Duhg's Army as long as Duhg converted exactly 4 other Soldiers of which G.W. was one.

How it is possible I've been blind for so long?
Bridge here is the key to playing Starcraft in Heroclix. Just welcome the uxm Brood Queen to the terran headquarters. We have even got a Kerrigan in the form of Invisible Woman. Add a couple of 15 points SHIELD agents on their incapacitate dials, a cheap leadership for the chance of taking tokens off the queen, and watch the swarm grow and expand it's glory through all the living existence.
It's true I got kind of recently my Brood swarm, and I've been out of the game for some years, but it still's shocking to me that this is not the first thing I thought of 8 years ago when I first saw the Brood Queen dial.

The very first thought I had when I saw the name "Brood Queen" was "hey, it's Starcraft in Heroclix!"

Though I have yet to actually do anything to make a Starcraft type team. But now I'm going to think on it.