There are ways of making liquid soap that don't require neutralization. We have some LS experts here to fill you in on the options or you can look up past threads. But here is the answer to the chemistry question:
There are various acids you could potentially use. You end up with the potassium salt of the acid, so you would have to be aware of the properties of the salts you are making (potassium salicylate, potassium glycolate) before deciding if you want to do it. Best maybe to be conservative.
I used lactic acid once, and the potassium lactate seemed to be good in liquid soap.
One thing you need to know for your calculations is how much KOH neutralizes a given amount of your acid. For instance:
The molecular weight of KOH is 56.1
The molecular weight of lactic acid is 90.1
To neutralize 1 g KOH you need 90.1 / 56.1 = 1.6 g lactic acid
Or the other way around:
To neutralize 1 g lactic acid you need 56.1 / 90.1 = 0.6 g KOH
If you use a good lye calculator, you simply put a 0-3% superfat into it, and completely eliminate the need to neutralize. Our online calculators ensure complete saponification. No more guessing at how much KOH to add.
I would also never suggest you dilute soap with anything except water. Anything else raises your possibility for growth of pathogens.