If Aloha kāua is 'hello you and I' and 'Aloha kākou' is hello everyone, can I infer that kākou is actually inclusive plural we?
Example of what I mean, kāua means we when there are two people and 'you' are one of them, kākou means we when there are three or more people and 'you' are one of them.
Perhaps I'm wrong, and I shouldn't assume, but if I'm right I don't think 'everyone' is a good translation in that case, it works with the context but only because you include yourself when you say 'aloha'.
From my understanding that is correct. However there are also "exclusive" first person plurals (the speaker and others, but not the person bring spoken too). So it's not because Aloha starts with yourself, but rather because "kākou" includes yourself. The understanding I got from the statement about Aloha always starting with yourself is that you should only use pronouns that includes yourself and your listener with Aloha. But it's the use of that first person multiple inclusive that makes it "everyone". Though I could be wrong.
You're right that kākou really does mean "we" or "us", when "us" refers to 3 or more people and includes your listener(s). But it it doesn't come across as very natural to say "Hello all of us" in English. You will, however, commonly hear "Aloha kākou" used in the same way that "Hello everyone" might be used in English, when speaking to a group or crowd of people, for example.