So, if it's not okay for me to buy their stock, is it okay to make them giving me a bunch of their stock part of the deal? Like "I will buy a billion dollars worth of your merchandise for $1.5 billion, and you will give me the merchandise plus $500 million of your stock?"
Yes because in that case you’re acquiring the stock directly from the company as part of a planned transaction. In one case you’d be dealing with individual uninformed shareholders which would cause a lack of confidence in markets (the entire reason insider trading rules were created), in the other you aren’t.
> Can I have insider knowledge about a company that the company in question doesn't itself know yet?
Yes you can
It's useful to think of this not as "insider knowledge" but the actual term: material non-public information.
Is the information you have material (i.e. will move the stock price)? Is it non-public? Then there you go: it would be ill-advised to trade on it.