- Should I bother to upgrade?
Definitely. QGIS is constantly under development. The latest release has several new features and I would definitely upgrade. General rule of thumbs:
a. Dont immediately update to a .0 release. So dont use 3.X.0, wait till 3.X.1 or 3.X.2 so the bugs are ironed out.
b. Dont uninstall the previous version that was working well for you until youve tested the new version. Sometimes your old scripts or plugins may not work on the latest release, its always worth checking before uninstalling a working version.
c. Dont upgrade if there a new version coming in the next few days. There is a timeline for releases her: https://www.qgis.org/en/site/getinvolved/development/roadmap.html
You can see that QGIS 3.10.2 is coming in within a couple of days. I would install that version, not 3.10.1.
- If upgrading, should I first Uninstall my QGIS Madeira?
Always test to see that your custom tools are all working with the latest version before uninstalling the previous versions. You can have multiple installations of QGIS without issues. In my testing, 3.10.1 is a good release and I have upgraded to it and uninstalled all previous versions.
- Will the new version of QGIS (Coruna) automatically find my Project files, and will it carry-over customized projections (coordinate systems) and so forth?
Yes, generally all your plugins, profiles and user data is saved separate to the installation directory. So you dont have to worry about losing data.