So to see them actually cross the line, you would need to purchase the ChEARs package. Basically there are big tall bleachers right at the finish line area, and those are for people who bought the package only. But those only cover maybe the last 100 feet or so. The remainder of the last .15 mile or so is first come, first served. I want to say a there are a few sections of smaller like 4 row bleachers just after runners leave the backstage area, and then a few small embankments between there and the finish bleachers. But there will usually be people packed 5-10 deep in areas trying to see/cheer for their runners all along that stretch.
As far as along the course goes, I believe the only other place that ChEARs gets you any special viewing is a space near the castle. I think that's new this year, but there are once again people 5-10 deep the whole way down Main Street up to the hub. But along course viewing you are limited for official/tolerated viewing areas. You can watch them at the start line, at the TTC, Main Street, over by the GF/Golf Course/Shades of Green, AK entry/parking areas, DHS entry area past BW, BC, YC, World Showcase and parts of Future World, and then finish line. There are a few other places people who have cars will hang out, but those are the only places guests can easily and safety get to using WDW transportation. Depending on your husbands speed you should be able to see then 4, maybe 5 times at most, less if you want to get a good spot anywhere. Cheer at start line, take monorail to TTC, cheer at TTC, walk down past Poly to GF/Shades of Green, cheer at GF/Shades of Green, head back to TTC, take monorail back to Epcot, cheer at finish area. You might be able to sneak in AK after GF/Shades of Green, but you may end up cutting it close to get back to finish depending on your husbands pace and if you get stuck in traffic due to road closures.