Glad to here you got one of your issues sorted out.
I am not fully versed in the newest units, but you should not be limited to 500 points by the GPS or your mapping program. The older units all had the ability to load 10,000 points in 20, 500 point segments. I have always used
http://topofusion.com/ TopoFusion is run by ScottM the creator of this website. The demo version will do what you need, first download a full track from Bikepacking.com then you need to use the Simplify/Split/Spline Track feature.
However big the downloaded track is, using the pan map (the hand symbol) right click and choose Simplify/Split/Spline track, first simplify it to 10,000 and then split it into equal pieces. Then it should all load into the GPS just fine. Using the free demo version you can only load 3 tracks at once and you'll be stuck with some of the map showing a demo square, moving the map moves the square so you can see everything if your patient.
Hope that helps
Tim