I haven't heard about the Y axis extension for the Taig that you mention. Do you have a link for it? Failing that, you might look at Sherline's new "Next Gen" mill, which has travels of 13.65" in X, 11" in Y and 9.38" in Z. 5800/5810 NexGen Mill - Sherline Products It certainly won't take as heavy a cut as a Bridgeport, but it's plenty heavy-duty enough for cutting aluminum. The table isn't very wide, but if you need more space for fixturing it's easy enough to mount a plate to it for that.
CNC gives you the ability to do a lot more than the simple straight linear cuts possible on a manual mill, but you can get these mills in either manual, DRO-equipped, CNC-ready, or CNC equipped versions. Generating G-code from your CAD system requires a separate CAM program, if CAM functionality isn't built into it. The choice of program depends on the sorts of things you're trying to make, but running a CAM program is generally not as difficult as CAD modeling - if you can do the latter, the former won't be too hard. As a prototype shop, you'll find all sorts of uses for a small CNC mill; once you have the ability to go directly from a drawing to a part. But you can do simple tasks, like cutting diagonal lines, by typing directional commands into the Manual Data Input (MDI) panel; this works better than hand-cranking for everyone but the occasional Etch-a-Sketch master.
You can order a complete system from Sherline (or from me, if you want a discount). They also have a wide range of accessories, which you can get pre-assorted in various packages or a la carte. It's a lot easier than buying something like a G0759 and launching into a CNC retrofitting process. Please let me know if you have any questions about these products.