The actual 3.0 release is still some time out (I am not in a position to say when, but my guess would be several weeks up to a few months). We don't have any kind of upgrade guide yet, but the
LoopBack 3.0 blog post describes the high-level changes, and you can check the
3.0-RELEASE-NOTES.md for some additional updates since the blog was written.
Upgrade timing is certainly up to you, but in general I would recommend waiting some time to upgrade a production app until a new release has had some time to "bake" to ensure all the bugs and wrinkles are shaken out (this goes for ANYTHING, not just LoopBack).
But it's never to early to start thinking about it, and understanding what will it will entail--I commend you for planning ahead!