I'm pretty new to creating tiled map services, but I'm poking around a bit in ArcMap and have a question. I have a very long path that stretches diagonally across Canada for about 700 miles. Within maybe 50 meters of this path I would like the highest resolution maps (level 19), but progressively less as I zoom out. At the full extent, I suppose level 1 or 2 would suffice. I plan to also expose a feature service for editing simple features including the geometry of the path itself, so ultimately, these tiles will need to be available for disconnected checkout. Now clearly I can't build a cache for all levels 1-19 as that would be terrabytes worth of data, and of course I don't need level 19 detail 100 miles away from my path either. Since the path is so long it's spatial extent is huge. So what is the best way to accomplish this?
Also, a projection question. The path in question (which I have as a lat/long .gpx file) actually spans 3 UTM zones. About 95% of it though is in a single UTM zone. Users in the field will have a hand-held GPS and if they are standing on the path with a correct GPS fix it should show the path obviously pretty much under-foot. Positional accuracy is more important than directional accuracy. What is the best projection to use for this type of tiled map service?