One of the first things I accepted on my DS918+ was, that disks will never be idle. So I packed many services (>20, most docker) on it + a raid1 M2 cache in front of the big raid5 (3x 8TB). access is quite low now and the power to spin the disks 24h per day is not wasted. DS918+ with 16GB M2-cache and its 4core CPU is a perfect thing to consolidate all those one-thing-solutions. I learned much by doing this. I still enjoy!
Next I will install 2 solar panels on balcony to supply some of the "basis power".

Osmand is my favorite app for on/offline multimap navigation gpx poi etc. BUT much features means much to learn for the user. So some other app may the better for you.

Maybe Phonetrack? I use that in combination with nextcloud.

https://gitlab.com/... (avbl. In fdroid)