Sadio Mane will probably really go to Bayern and he would also fit well in there team. There are even rumors that Bayern want to sign Cristiano but I can't imagine that. Lewa's departure will weaken Bayern a bit and they need a good replacement for him. Very exciting!
I absolutely do not believe in such a transfer (Ronaldo to Bayern), but I would look at it with interest - I think Ronaldo, even at that age, would try to surpass Lewandowski's record.
Nobody would like to underestimate Mbappe in any way for sure. However I don't see him as the number one player when we take Messi and Ronaldo's primes into account. I'm not a PSG fan but I wouldn't still say so even if I was a PSG fan. It is the truth that Mbappe is still very young and he has long years ahead of him to improve himself even more. I guess that he needs to leave PSG and join a team like Real Madrid to get close to being the "number one" in the future. PSG don't seem like they will have a very bright future full of titles except the Ligue 1.
He's not that young either. He is already 23 years old and although on the one hand he is a world champion and has achieved a lot, but in order to stand on a par with the greats and get a bunch of golden balls, he needs to start doing it right now, otherwise you can stay in the category of huge talents who have not fully revealed their potential.