Hello,

2 L3t and 1 L3s will work great - especially with the StageScape mixer, because it is meant to be a system.  The feedback suppression on the mixer will work throughout your entire system, and with the L6 Link connection with AES/EBU cables (recommended up to 50' of length), a graphic equalizer can be placed on your main outs.   The L6 Link connection will also automatically configure your left and right speakers, and you will be able to control the crossover frequency to your sub from the board.  You can also ping your speakers, which makes the speaker LED light flash, in order to make sure your left is left and right is right.  Another possibility would be to use L3t's as monitors and still utilize the sub for extra low end. 

I've used this system for a number of band rehearsals and have not had a problem.  Our drummer is pretty loud.  Plus, with 2 guitar half stacks, an 8 speaker bass cabinet and 2 microphones - I have yet to hear feedback.  The system is loud enough to keep up with the amps and drums, and can probably go louder than we would want to. 

With that system I would be confident to walk into any bar/club/park and have a good show with very little worry or hastle about the setup or sound system.  The sub is of good size, but small enough to fit into the trunk of my Crown Victoria with the L3t's across the back seat with enough room for other passengers/gear.  Very ideal for practice spaces. 

I hope this is helpful.

Jon