It’s totally possible to upgrade in stages if that’s what you want. The Changelog entries include the revision for each repository, so if you
git pull in each (
phabricator) and then
git checkout the right revisions, you’ll have your whole setup at a consistent point in time. Then you can
bin/storage upgrade to get your schema up to date to that point in time.
The update process has always been smooth and painless in my (extensive) experience running Phabricator, so I don’t expect you’ll have much difficulty.