Is there a "better" translation for "你我还没完呢"? Why is it "你我" without a possible "和"? And please can anyone confirm the function of "呢" in this one?
The translation is accurate. 没完 means that there will be a continuation, and 呢 adds to this.

Translations are not and should not ever be word for word, but adapted to the linguistic context. Chinese is not as wordy as, say, American English, and there is simply no need to sprinkle the text with repeated instances of pronouns (like 我) or words that can be inferred by context.

你我 is very common.