Do we have 1 free foreign squad spot currently? If not, it makes some of your options (Messi+Aguero/New striker) unlikely. I can't see City forcing an exit of any players not named Mendy this summer - moving players on huge wages is too difficult on the current market, and City rarely do that anyway
If Messi comes, he most probably replaces Aguero, and that's it. If he doesn't sign, we probably extend Kun for a year and wait until 22 when new opportunities will arise (for example, Mbappe's contract ends that summer)
That's how see it, though the reality could be very different. As for an orthodox No9, I don't think Pep really needs such a player - versatile forward like Foden fits CF role better for me