Motor - Titan 12T (12-Turn - 550 size)

Yes this will increase the speed slightly.

HW86080120 or P-CC111400 should do the trick

It's the same size but lower turns, so yes will be quicker. I'd not run 3S however 

Yes that should be OK

Motors are inherently fine with water - but you must ensure they are thoroughly cleaned and dried after wet use

Not quoted sorry

Yes, it's standard size so should fit that model.

Yes it should fit the Carnage. It's 12T so will be an upgrade over the 15T stock motor, however the stock ESC won't handle that. You would want to upgrade the ESC to say HW30120201

You can use:

• TRX2416 Gear, 16-T pinion (48-pitch)
• TRX1918 Gear, 18-T pinion (48-pitch)
• TRX2419 Gear, 19-T pinion (48-pitch)
• TRX2421 Gear, 21-T pinion (48-pitch)
• TRX2423 Gear, 23-T pinion (48-pitch) 

Standard 1/8th inch / 3.25mmshaft diameter

Uknown sorry, Traxaxs don't quote RPM on this motor.

It's a 550 size, so a little larger than your standard 540. We'd recommend sticking to a 540 size motor to avoid any fitment issues.

I believe the super sport motor is around 23T, so yes - a 12T motor would be much quicker, but you'd need to check that your speed controller could handle it.