If I install from somewhere other than the play store, can I still update from the play store later, or will I have to uninstall and reinstall again?
I haven't personally testing switching app stores as I have F-droid installed for other reasons and just intuitively used it from the start for jerboa. My belief though is that anytime you switch sources for an app, you're best off uninstalling/reinstalling... and with Jerboa the worst side effect of that is having to re-login.
... but since I also have other Lemmy apps installed to use in the meantime, I've been figuring I'd just wait it out...
This is a perfectly reasonable choice, just wanted you to know what it took to get Jerboa doing it's thing again. If you have other ways of using Lemmy you're satisfied with, have at it.