Base maps are a waste of time. Open Street Map will get your going nicely though (for free)
I bought a non-HRM 810, works fine with my HRM
This ^^^ is exactly what I did. Love my 810*, way better than my old 500. The openstreetmap stuff works really well. I just plot a route in BikeHike then it’s easy enough to follow on the Garmin (provided you turn off the automatic routing.) I hate stopping to look at maps so this is brilliant for trying new routes.
I’m not sure about the Strava stuff. Could easily derail a disciplined training ride!
(*) It has had a few funny moments. e.g. resetting itself, going back to factory defaults and losing all my bike and activity settings, etc. But on the whole these are very infrequent and it is a great product.