Steam-Powered weapons

Well, with steampunk you've got a lot of latitude. The steam-powered tank is certainly plausible. I'm not so sure about the exoskeleton.

You could have a lot of fun coming up with things, for example, a steam-powered "horse" (that is, some kind of machine that's ridden by a rider); a catapult with multiple slinging arms; some kind of crude steam-power, dragonfly-like flying machine (that maybe only gets 10 feet off the ground); a steam power "train" that lays its own track in front of itself; and perhaps instead of an exoskeleton, some kind of steam-powered, personal one-man tank (I see it as roughly triangular shaped where the user stands up in it).

Just throwing out another idea . . .

Rather than having it mounted on the user's back, you could have it so it was a two-piece type of thing. The user is wearing the exoskeleton itself, while there's a small wagon-like (or bug-like) contraction following behind. The wagon is the power supply, and attaches to the user by some kind of tube or mechanical means.

A steam-powered amphibian vehicle that looks like a cross between a frog, the fuselage of an aircraft, and old steel-wheeled tractor.

By the way, I used to own an old steel-wheeled tractor (from sometime before 1930). It didn't run but it could have with some work.

You'd be better off using a kilogram of uranium rather than coal. The coal wouldn't be enough to get up a head of steam to boil 10 gallons of water.

A steam powered suit would get a little hot don't you think. Have you ever been inside a steam powered engine room? It's always over 120° F, sometimes as hot as 140°.

Yeah, a steam-powered one-man tank sounds more workable. Methinks you'll need some hand-waving to explain any workable degree of energy efficiency--some wonder alloy that is uberlight yet sooperstrong, a radical engine design, etc. As for the heat--tubes filled with dry ice surrounding the driver maybe? I'm just shooting from the hip here.

Lots of steampunk has robots that think and such. As long as your story is internally consistent it's fine. Just don't have robotic exoskeletons but they can't figure out how to do simpler things.

If you read Stephen Hunt (great ideas but mediocre stories) he's got some good ideas, the steam-men (steam powered robots) have guns that use a gravity feed of lead balls like a paintball gun which fall into the barrel of a gun which has a high intensity stream of steam blasting through it, creating essentially, a machine gun.