1. Get a folding hand cart like this:
2. Get a markbass LMII/LMIII or perhaps gk mb500
3. If you're going schroeder go for the 15L. I played thru a friends 12L and they are *tiny* ...maybe the size of 5 phone books stacked.
If you really need a super small cab I doubt you can beat the size of the 12L but you have a trade-off in terms of tone.
Regarding amps... I have owned about 5 schroe cabs in the past and from my experience they like a very warm, bass-heavy amp. For that reason I would rule out the genz benz stuff as both the gb amps and schroe cabs are weak in the lows. I've owned both the shuttle 6.0 & LMII with a scrhoe 1212R and IMO/IME the LMII sounds much better with the schroe cabs... espcially because they have their bass eq set at 40hz which can really beef up the schroe cabs. I'd also pickup a Tech 21 VT Bass pedal. That thing makes any amp/cab sound great IME.
Another option you should seriously consider is the markbass 121p. Its a great sounding 30LB 112 combo with the LMII built-in. Just throw that on a hand cart and thats all you need. Perfect for the subway and sound miles better than the 12l. Later on add another 112 8 ohm cab and you have a rig that can handle most small to medium sized venues.
BTW, if you do decide to go the seperate amp/cab route an LMII will fit combfortably in a Warwick Rockbag softbass case.