In answer to your first question, I would ask 2 others.
- How prominent are the creases in your maps? If not too significant, I would consider a high resolution scan. When I scan a board, I usually do it at 600dpi.
- How well does you system manipulate large graphics files? This is where it gets tricky. The individual scans will be quite large. When I do a PG board, I trim and stitch 6 scans. That makes 400+ MB open file.
If either of those questions result in an unpalatable answer, consider making a new map.
Assuming you made a scan, I like to use GIMP to stitch the scans together. I put each scan on a different layer. Move the layers up and down as needed. make an alpha channel layer. Trim the canvas to that layer when you are done. I'll often change the resolution of the final image to make it more manageable, but still visually acceptable.
Large prints are a quandary. I've found
Poster Razor to be a useful tool for sectioning a large map. If you want to be particularly creative, you could make paper map, then mount it like Avalon Hill used to do with their games.
The this is another question of how deep do you want to go. Foam boiard should work fine. I would probably section the board and make hinges with white paper tape.
