Try what you own first.
Another way to do this if you like your m43 is to take over-lapping photos with a longer lens then assemble in PS or editor of your choice to get higher res.
Though I haven't printed too many larger images with my m43, I can tell you from experience that even using my 6-10-12 mp dSLR cameras, I've printed many, many 20x30 and 24xx36 prints and canvas prints and the quality is stunning. You may be able to do likewise, especially with the quality of today's lenses and sensors.
Until you do your testing, even a section from a larger print file (you can always tile and reassemble your prints), you will never know how well your crafting of your image will hold up. As always, your results will vary.
Very true. I have done plenty of stitching in the past, but generally I find it more annoying than helpful. I prefer (and this is a personal preference, nothing technical) to get everything in one shot as much as possible. Since I can do 13x19 borderless, it should be no issue to do overlapped prints.
I really would hate to give up the great feel of the E-M5. Honestly, it's a camera that allows me to love shooting again.