Routable Bicycle (Openfietsmap Lite) issue

I’m working on creating a circle route for a cycle tour from the Twin Cities (USA) to St Louis, Santa Fe, Yellowstone and back to the Twin Cities. I want to create the route in several segments so there are no issues with it being too large. I specified tiles from Twin Cities to St Louis, then downloaded. After downloading I renamed the map TC_to_StL (the .exe version for windows). When I open the file it asks whether I want to replace the earlier openfietsmap. I don’t know whether I do or not, but it seems if I create five or six maps for my route and try to install for Basecamp to read, each one will replace the earlier one, even though the maps have different names. What am I getting wrong?

Why do you fear that a complete map would be too large?

Renaming the install file doesn’t change anything. Each of the maps you download still has the same family ID and is installed in the same location, so they’ll keep getting overwritten. If you want to have multiple separate maps installed, you can use Javawa GMTK to rename one map before installing another. The easiest thing to do, though, is just generate a single map that covers the entire area you want. It’ll make things easier to manage and use.

I’m just starting to familiarize myself with device. I read that creating a route can result in too many waypoints. That makes the make nonfunctional? So I’m assuming I need a handful of routes instead of one large one. Is this not correct?

If I create a route using basecamp or mapsource, is that then individually named before uploading to the device? Does that work, whereas simply uploading a map instead of a route does not? To answer my own question, I would think I would be uploading a file instead of installing a program, so filename would make the difference?

To create a route in Basecamp or Mapsource you need a routable map. So, your first step is to install a map that covers the area you want to travel. Next step is to create the route, finally you can select the map tiles needed close to your route and create a singe gmapsupp.img for your device and you can also transfer the route.
Just a hint:
My personal preference is to create tracks instead of routes, and I prefer to do that in Brouter:

I fiddled around and created a route from TC to StL (using the routable openfietsmap lite with tiles selected for the route). So, doing that as a track instead, I would then save the track as a gmapsupp.img and uplod to the garmin? I don’t see a “save as” command, but I suppose that may be buried in the uploading/transferring process. Also, thanks for the brouter rec, but I don’t see that it has cycle paths like MRT (Mississippi River Trail) or the Katy Trail. Am I missing something?

No, you have to save a track as gpx file, not as gmapsupp.img, this format is only for maps.
Uploading tracks to your device can be done with Basecamp or by simply copying it with a file manager to the GPX directory in the garmin folder on your device or to the micro SD card.

Did you try to change the map layer to OpenCycleMap (icon in the top right corner)?

I did spend a little more time with it this morning before coming back here to check in. Excellent resource. I had missed the layers in the upper right corner. OpenTopoMap with Cycling (Waymarked Trails) appears to be the best combination. You are correct, it’s better than

Just to make that clear: I prefer it for planning the route / track (the gpx) because it offers better options than Garmins software, but I still use the openfietsmap lite style for the maps on my Oregon.