Vinyl cutting needs: A way to hold the thin material flat (vacuum surface) and you need "tangential" cutting and things like blade offset. A drag knife (swivel) could be used but it needs to "float" or you just cut through the 2 to 3 mil vinyl and then through the backing (not good!). As cheap as vinyl cutters have gotten (like the ones from USCutter) it does not make sense to try and use a CNC table to cut vinyl. The models that have the registration mark sensors built in are nice. It would allow you to get vinyl multi-color printed and make professional decals then contour cut them on your machine.2. Vinyl/Stencil Cutting - For cutting vinyl stickers and spraypaint stencils for marking the equipment I produce. This doesn't seem like it'd be too hard, I simply have no idea how this sort of cutter is supposed to work.
Milling aluminum is different than doing wood routing, is different than doing plasma and is different than doing vinyl cutting. You are correct in your observation that they are all basically the same thing (XYZ motion) and can all be originated from the same or similar software BUT it's the final process that makes all the difference. It's like wanting to build a High Speed Sport Dump Truck that floats. You can do it (the ARMY has all kinds of neat multipurpose vehicles!) but each one will be a compromise so you end up with a machine that is either very expensive or does none of the jobs very well.3. Wood Routing/Aluminum Milling - If I could get both plasma cutting and light-duty milling in one package, I'd be in heaven. Wood routing would be for producing furniture (for myself). Aluminum milling would let me take on small jobs from my physics professors. I know most of them pretty well and they often mention needing some odd part for their lab work (not necessarily with ultra-tight tolerances), which they can't get from the campus machine shop because the shop is always overbooked and overpriced. However, this would probably be the hardest feature to add, and it's getting furthest away from my original goal of producing fitness equipment, so I'll probably drop this.
Just like in physical training there are different machines that are better than the one-machine-does-it-all like the Bowflex approach.
It's easy to let your excitement in CNC get you in deep water faster than you want.