If I were you, I'd join the homequiltingsystems group at
http://groups.yahoo.com and do a search on "thread cutter" there. It will give you an idea of the advantages and disadvantages of having a thread cutter. If you're still not sure, you can ask for opinions on that group. Someone there is bound to have this setup.
I'm not sure what difference a larger table would make unless it allows you to quilt larger quilts. If you mostly quilt small quilts, it may not add any value.