Living Car Free - Xtracycle and Trailer?

I have a Toyota Previa (a minivan I guess, for the Americans), which is old and inexpensive, and I need for certain things. I also have to have a car for my job (I'm a salesman), but I'm trying to avoid driving it altogether for most things. It's expensive to run, being a minivan, but it's the capacity that I need, so the obvious solution is, only drive it when it's absolutely necessary.

At the moment, I cycle for everything except picking up and dropping off my son (I'm divorced, and when I pick him up from school, or from her house, there are practical reasons he can't ride), and doing our main grocery shop. An Xtracycle is rapidly starting to look good value - I'm sure it would pay for itself within a year just doing those runs (I'll hook it on to something I pick up cheap), and if I start to factor in giving my girlfriend a lift when we go into town, rather than paying for fuel and parking, it really sounds good.

My only issue is, I'm not sure that even an Xtracycle will always be able to carry all the shopping etc. Is it possible to run a trailer behind an Xtracycle? Also, when the panniers are loaded, is it still possible to carry a passenger on the snapboard thing, or do full panniers interfere with the footboards?

Yes, a trailer can be run on the back on an Xtracycle. Depending on the trailer you may have to get creative; the Xtracycle folks will help you figure it out if you ask, they're quite approachable.

Depending on how loaded the Freeloaders are, and how small the passenger is, you're fine. Two bags of groceries, a backpack, and an adult woman is about as much as I've managed in this way, and you could probably do four bags of groceries with a kid.

You might find yourself surprised by how much you can carry on your long bike. Consider getting a set of Wideloaders and you may not need the trailer at all.

That's worth consideration. I've got to put the money together for the Free Radical first, and find an appropriate hybrid/mtb to put it on!