Well, the quilter's cruise control certainly adds another variable. Personally, I found it impossible to quilt without some sort of stitch regulator -- at the very least, it shortens the amount of time it takes to get decent with your machine setup. Without it, you're much more likely to have stitches of different lengths; moving at a perfectly uniform speed and not slowing down or speeding up while going around curves is very difficult! I know some people can do it, but I'm not one of them ;)
You don't need to upgrade the carriage immediately -- the frame will work fine without it, so don't stress too much about that; it's just one of those things that is nice to do once you've worked with the frame for a bit.
If one of the used setups that you're thinking of buying comes with frame, sewing machine, AND stitch regulator, personally I'd go with that one. You'll be able to start out immediately with that setup, and you'll probably have much less initial frustration.