Interestingly my first introduction to a Taig mill was buying one to use for a laboratory experiment. Glad to see other laboratory uses of a Taig. In my case I was so impressed with the Taig machine and the folks at Taig that I wound becoming a dealer.
First let me say that the 4" vised you linked to is way to big for the Taig. The vise that Taig provides is a bit tricky to use but very useful. I also recommend looking at the screw-less vise that Sherline makes. For larger items you will likely find that using other clamping methods is more advantageous. I really like the toggle clamps make by A2Z CNC and include at least one set in starter kits.
I would also recommend getting the 5 piece bit set from Taig to start out with, and perhaps a fly cutter, and a few extra spindle belts. Oh yes the Edge finder Taig sells is the perfect size for the machine also.
The 4th axis on a mill is handy for lots of things. If you have a lot of turning work to then a lathe will make the job quicker. It is also possible to mount a Lathe style headstock to the mill, and tool posts to the bed and make a sort of vertical gang lathe. The programming is a bit complex, but it can work well for some things.