For the design aspect, mechanical things can be as simple or complex as one wants, see:
if your wife wants decorative things, then maybe she could at least do a sketch? If you then ink over it in Sharpie it should trace quite well:
Correct, the machine needs to have a computer connected to it via a USB cable when in use — some folks get an inexpensive Rasbperry Pi and leave that in the shop, other folks get a used laptop (some luck into a rugged one) and leave it connected — other folks will use the same computer used for designing in Carbide Create to run Carbide Motion, and just carry it out to the shop and plug it in.
For a long while, inexpensive fanless Windows tablets were a thing, and being sealed, they were well-suited to the rigors of a shop environment. Since Carbide Motion is moving to 64-bit, the less expensive computer options are getting left behind, we’ll have to see.