Great post.
I suppose the glaring issue for me defensively while using this system (with current personnel) is the space behind our wide players, particularly on our right flank. We'll be asking our RB/CB to tuck across toward the centre, and given that Bailey is not great defensively, it leaves an ocean of space between our 'full back' and RM/RW on that side. I know we have and will ask McGinn to come across to cover that, but that stretches the midfield somewhat.
For me the recruitment of a RM/RW is therefore vital. We need someone with an engine who can contribute to the attack, but is not so attack minded that they cannot bomb back to cover the RB/RM position. This is why I thought Guendouzi might be perfect for us, sitting a little deeper on that side and capable of both aspects of play.
I appreciate where @CVByrne is coming from though. It's not as simple as this, and we need, and will have tactical flexibility, but the right hand side still worries me with the way we set up at the moment.
The other thing we need to consider is whether we want to sacrifice any attacking power to address this. Maybe we don't address it at all, acknowledge it as a weakness, but take a calculated risk to cause the opposition problems.