A question on squad numbers..

So the Codex says that for every 5 models in a squad of wracks, one wrack may upgrade to a liquifier. Does that mean if I use 4 wracks and a haemonculi, I can have 2 liquifiers? (one on haemy and one on a wrack)

Would this be plausible in order to keep point costs low and get a close combat squad in a venom?

Edit: Would also like to ask, what other wargear should I grab on the haemy? Liquifier and scissorhands? What about a huskblade or agonizer for the close combat or a stinger pistol?

no, as a haemionculus is not a wrack. Attaching ICs happens at deployment, so your wracks were not at 5, and could not buy the liquifier in the first place.

Sadly, no. Think about that You check unit size before adding IC.

As for Haemy... cheaper=better. I guess Venom Blade + Liquifier + something is way to go. Stinger pistol is also OK (and cheaper) but I would rather take flamer.

Just to make this as clear as possible.
As was said before, you can take only one liquifier in the mentioned unit and you have to take this one with the Haemi.
If you took 5 Wracks and a Haemi you could take two and if you took 10 Wracks and a Haemi you could take three.

When the Codex mentiones 'for every X' it means for every completed X, not per X or part thereof.
This comes into effect, because the Haemi is an Independent Character and so becomes a part of the unit of Wracks the moment, they are deployed together. So before they are just 4 Models and can't take a liquifier. After, they were elligible, but it's to late to add one.