My plotter mostly just sits there. Every once in a while I will cut some window lettering, but practically everything else is digital printing, which I outsource. Get a subscription to SignCraft magazine, and familiarize yourself with the specific niche of the "craft" based commercial sign industry (where art is just as important as fabrication). Hook up with some quality printing and fabrication companies, and find a local company that can help with installations (digging holes, boom truck and crane work - you will be surprised how fast this will come up - the easy stuff people will just do themselves). Electric companies can be good partners as they have the equipment but will generally not be competitive for signs (and they can hook up lights).
Maybe more important, I would recommend learning Corel Draw. As an artist you will appreciate what you can do with it. Vinyl Master functions as a "bridge" program, translating vector art to a cutting path. Corel will offer boundless creative opportunities, and you can order anything you create from companies like FireSprint and Signs 365.
If your goal is to be a design based business, you will need to distinguish yourself with the uniqueness and quality of your designs. Fabrication and installation can be outsourced. If you want to be a production and fabrication business, you will need to make a considerably bigger investment in order to compete with the multi-million dollar facilities selling banners for 89¢ a square foor on the internet. Electric sign work, installation and maintenance will require at least several hundred thousand dollars in investment and significant training.
As a tattoo artist, my guess is you will be coming at this from the design angle. Plenty of potential there, and with a good marketing plan, a killer portfolio (and a lot of hustle) you will be fine.