I am in exactly the same boat...big combo Brother machine, and the desire to take classes. My combo machine is great at thick seams, but it is a heavy critter, and even with a rolling tote it is a bit much to haul around. I set out to find a smaller one made by the same manufacturer, in the belief that they would be somewhat similar to operate, but even more importantly will share feet.
Two days ago I found a smaller Brother machine on Craig'sList. Using an electrical inverter, I was able to test the general function of the machine in the parking lot where the seller and I met up. But I have been too busy since then to test the feet theory. Keeping my fingers crossed. Also hoping it handles thick seams! But I paid very little for it, so it won't be a great loss if not.
So, my suggestion is to find a smaller version of what you already have.....