+ 1 on JTS....and on the "make sure it fits" point.

Aluminum can feel a bit stiffer, and be less comfy for very long rides. Trade off is they can feel snappier, like all the pedal energy is going towards acceleration. Longest ride I've had is about 65 miles, and i was hurting. But I'm not sure it would hurt less with a different frame material. And, to confuse matters, it's not like there's one kind of aluminum and one kind of steel. They can vary quite a bit in quality, weight, feel, flexibility from one "alu" bike to another.

Cross bikes are overbuilt to deal with the rough stuff, and a little more "compact" than roadies (as in the top tube tends to be shorter, so you sit more upright).

I tow a burley, but have never tried it with the JTS (i reserve it for commuting, winter fun and long summer rides (with a second wheelset and roady tires). I come in around 230, and have done the commute with 20 pounds of laptop etc.

Re carbon...I chose not to. The way it fails on the occassions when it does frankly scares the !@^$!#% out of me. Catastophic fork failure? Because I nicked it a month ahead and weakened it without realizing? Not for me. But, I'm weird that way, and if you're careful with your bike and inspect it carefully, go for it. I'm just weary of major manfacturers telling you to swap out carbon parts after X years, regardless....I keep thinking there must be a reason.

As long as the wheels are good (32 spoke minimum, tough hubs, etc. -- stock on JTS is Mavic open sport, which are among the toughest) and the bike is comfy, cross would be a good choice for what you describe.