To begin with your first question "About the work area, is the same for printing than for cutting, milling, and so on, right?"
Yes your working area is within the limits of your machine, however keep in mind that your max. Z-height changes by the extend of the accesorie tools.
A 600 has a Z-heigt of 140mm maximum and that is from the bed.
How much does the nozzle extends the mounting plate? maybe 15mm
Than the heating bed the size is know but the hight is a question? Lets say 20mm probably more.
Than your maximum printing height is reduced to approx 100mm
And the cost of the printing module + heating bed + cooling van is about € 479.00+ € 149.00 + € 30.00 = € 658.00
You can earch for a larger heatbed on the famous chinese sites, but that will give even more unsertanty.
If you want to go for 3D printing buy a dedicad machine .
They have a larger printing area mostly approx 210 x 210-250 Wide x 190-210 Height
Has its own proven software.
You can keep milling or whatever on your steppie, its not occupied:)
Price is not much more expecive than the stepcraft solution.
Oh and don't forget the time a print takes to complete, I made relative small prints that take more then 6 hours.
And even complexer models can take up to 20 hours to print. I don't want my steppie to run for such a long time.
I think you are right, at first I thought on this CNC like a flexible machine, but in this case the best is to use the money of the printing module for buying a 3D printer.
I pretend to use the stepcraft for doing PCB prototypes and cutting vinyl and so on, and I can use the 3D printer for doing the cases for the PCBs, so I could do both pieces at the same time.
I think you made the right decission.
I once had to make the same choice and I choose for the original Prusa I3 Mk3 printer as a kit and it includes all the software you need.
Until today I have no regret of that chioce, maybe al little bit more expencive than the clones, but very good support and frequent updates of the software and firmware.
I use it for RC modelbuilding, including PCB housing and even gears.