Dude read my reply to this thread. I may be on to something but idk. And Zabuza can more than likely create his own source. Lets be logical here, Fodders were able to use Water Wall, a B-rank tech. If Fodders can make there own water, then Zabuza definitely can. I mean, Zabuza was shown to use A-rank Suiton and Water Wall is a B-rank, clearly he has the skill to use it. Water Trumpet, a C-rank tech considered a BASIC Suiton requires the user to expel their own water from their mouth. It wouldn't be basic if doing so was hard.
I mean come on dude, you're a smart guy, isn't it pretty obvious Zabuza can make his own water? I mean, Suiton is his affinity and he is above fodder level
While you would expect him to be able to going off of part 2's power scaling, it's hard to estimate which techniques he would be capable of without a source. It's speculation at that point.
You'd have to find some middle ground with someone on what they're willing to give Zabuza. Does he get Kisame-level feats with suiton? Mei? Just give him the ability to use Suijinheki without one(it's all Kakashi and Darui have shown without a source)?
On top of that, one of Zabuza's techniques that he showed with a source, and the only one that would probably do anything to Chouji(Daibakufu) seems to be impossible without a source. You would have to have Kisame-level feats of creating any amount of water you please from your mouth to pull that off without a pre-existing source.
Zabuza lacks the firepower, giving him the ability to create his own suiton or not, to take out Chouji. Creating that many clones could backfire pretty quickly, especially if Chouji blows away the mist. You're exhausting a lot of Zabuza's chakra at that point.
To fight someone of Chouji's size, you need a some kind of high powered piercing jutsu/weapon(like kusanagi, raiden, raiton-infused weapons, etc), pure strength(like Kakuzu, or someone with gates, summons, etc), or hacked techniques(susanoo, amaterasu, shinra tensei, etc).
If you restrict Chouji to his base size, Zabuza would probably be able to take care of it with silent killing, even with Chouji having his BM. It's just the size that's an issue here.