This would be a personal preference. You may open up a new can of worms by upgrading Plesk, who knows. If you have a nice backup/restore strategy in place, backup and update to 8.4.
The Plesk version doesn't matter for you. The only issues I can think of with psa 8.2 or 8.3 is Horde messing up, but the fix is listed in ART's wiki.