I know it's hard to find the right strategy, Real and others haven't yet either. I think Real will eventually buy Mbappe for +300M, maybe 400M and that would be a great buy, but the waiting time until could still be trophyless, which is also expensive. Liverpool bought lesser players and WC coach to make them grow into a team. That is a great strategy but hard for a club of our size to do. As you, I hope we will try around the time when Messi leaves.
Don't think RM will pay anywhere close to 300m for Mbappe. They'll wait until 2021 when he'll only have a year left on his contract so PSG won't have much negotiating power and they'll sell him for whatever they can get or risk losing him for nothing. Of course all this assuming Mbappe wants to go to RM and only RM and he won't renew his contract which PSG will undoubtely offer him to do (there are rumours they already have).
You're right so far, but Dembele and Coutinho will be defining for this story-line. It is not utopia to see desperate Chelsea, desperate Arsenal or manic PSG pay 100M for each of those players, which would be great sales right now. So, jury is still out in terms of how bad we are to sell players, imo.
I think we'll be happy to get 100m combined for both of them.
I don't believe Chelsea is really as desperate. They have a lot of their own young players breaking through (transfer ban did them a big longterm favour in this regard imo) and if anything they'll probably prefer to sign someone like Sancho. They would probably take Dembele for 30 or 40m but not for more. Arsenal can't afford their wages so PSG is probably the only option but I'm affraid we'll include one or both of them in a possible Neymar deal which would bring us other even bigger problems longterm. IF there won't be any serious offers I prefer to loan Coutinho and Dembele (if it means not getting Neymar back) just to get rid of their wages. We need to do something about this big problem imo and not making it even worse by getting another big earner like Neymar for some crazy transfer fee which would also prevent us to address other needs (a midfielder or two and a CB).
Håland could come winter 2020 for 75M if this summer becomes a disaster-Neymar-summer once again, and I wouldn't be against that. Lautaro would most likely be part of lower price for one of our players (Vidal, Semedo) in exchange, but still too expensive as you say. The other names sound fine, but I think we should also aim for more De Jong-like transfers, not only less profiled transfers like Aouar or Soumare would be.
IIRC Haaland's clause is only for summer 2021. Wouldn't make much sense for Dortmund to sell him in January.
I would put Aouar's possibly transfer almost in the same category as FDJ's. Yeah, he didn't have that breakthrough season in the CL yet like Frenkie did last season but he has almost 100 appearances in Ligue 1 while FDJ only had around 60 in a worse league (and playing a lot as a CB in 2017/18 season) before we've signed him. So he basically had only good 6 months (since we've signed him in January before he put up those great performances against RM and Juve) as a DM in Ajax before we pulled a trigger. Aouar will have 3 good to potentially great seasons in Lyon behind him this summer and he's also a year younger.
I agree Soumare would be a lower profiled transfer but he could still do good for us.