By my reading of the beast conclave feature, the wolf gains hit die and levels as a player does. It should have 5.5 hp per level if rolling or 6 if taking a 5 on its D8. Assuming the latter, wolf 5 should have 29-30 HP, or 27.5 otherwise. Unless it has 2D8+2 hp when you get it and doesn't gain its third hit die until you hit level 4.
But this is a pretty minor point. It isn't something I would do just because the beast will get knocked out by one stray breath attack with HP that low. You'll be resurrecting it all the time.