Before you select any piece of equipment you have to determine the market you will be serving. Will you be able to offer installation and maintenance service to corporate entities, or local maintenance and installation to small businesses? This will help determine the type of fabrication equipment you need. The unique advantage a local sign shop has over any sign provider that is miles away is location and the economies of local installation and maintenance.
Considerations of local code and insurance requirements will help to determine the feasibility of your investment in service equipment and personal. The scale and scope of your contracts will help to determine space and material handling requirements. Local competition should be reviewed both for feasibility and pricing. Knowing the existing conditions of your market is essential.
Buying a printer, at this point, is a trivial consideration. One decent service truck can cost $100,000 or more; the cost of your physical plant, service fleet, and personal are your first considerations. There are plenty of trade printers that will service your printing needs for less cost than you can do it yourself.
All that said, you may have a business plan that does not include installation and maintenance. You may be a design based company, or apparel printing service that wants to add stickers, posters, and small banners to your offerings. If that is the case, I would strongly advice searching the internet to see what is already available (at the click of a button). You may decide that out-sourcing printing is much more feasible.