Hearthpwn

A single Vampiric Blood can give you +2/+2, which is very likely to happen regularly. Now imagine a Blood Boil, which can give you +7/+7 if it hits a full board. There's some really good potential for this to give you a huge Lifesteal minion in the mid-game. Besides, you can even wait a bit before using your second attack just to capitalize on the minion. And you can use it in conjunction with Unholy Frenzy very easily to heal up a lot and potentially resummon it! This weapon has insane control potential!

Is there max stats?

If it's consistent with other such cards, then there isn't a max on this.

So it's at minimum a 3/3 assuming you attack minions with the weapon.  Going to be annoying to get it much higher than that.

At its base, 3 mana 3/2 "Summon a 3/3 undead and gain a corpse" is already stellar, since that's 3 mana to trade with 3 bodies ( Your 3/3 trading as well. )

If you can play vampiric blood alongside it, that's a +2/+2 on that body. This is a really strong control tool that helps make up a little for the lost of Renathal.

Blood DK's have several ways to change their life total either healing or damage wise.  I see the 2 swings for a 3/3 to be the minimum if this is playable.   Turn 4 options include Vampiric Blood ( 2 ticks likely), Noxious Cadaver. Death Strike  Turn 5 options include Blood Boil ( up to 7 ticks if you're behind on board).  As well as a bunch of others later where this loses effectiveness, but if you need a big lifesteal chonker on the board this could be the way

So if you swing at minions you're at least guaranteed a 3/3. That seems alright. Viability may depend on what the meta looks like, if a 3 attack weapon has any good targets on turn 3.