The i7 (3615QM) in it holds up extremely well. The storage was catastrophically slow but the system allowed me to effortlessly migrate over to an external SSD (then using the internal storage just for time machine backups).

Finally considering upgrading as it has been a while.

The low power consumption of the thing is one thing that always just blows me away. No noise, at all. My UPS seems to last forever when the power does go out.

Yes, you could only compile once, but as soon as you add new native modules, you have to recompile the whole app. But you can basically use any other OS to write RN code. If you don't plan to add new native modules to it, then you can compile / deploy your app once from a Mac, then use CodePush to remote update the JS which can be done from any other OS.

Yes but it’s the oldest model supported by Mojave, so consider getting a used 2014 maybe if you want it to be relevant for a few more OS releases.