That's quite a few big ifs.
Current club don't seem in a hurry to release him.
A dof who is in another job.
A player buying in. Question marks over his buy in to the past two managers
Funds not having CL will affect.
Current club won't release him until he finds a new one. So that's not even an issue.
If he's as detail-oriented as it is rumored, however, he will take a good look at the squads of any team he would be joining. I know I would be studying tape and identifying which players suit my ideas, what their potential seems to be, what the best system for them is, what gaps there are and how much it may cost to fill them, how would I cover for player A or B leaving, etc etc.
So, if I am negotiating with Spurs for example, I will have a decent idea of the existing squad quality and how I could best use it, as well as what positions need strengthening. I will then discuss all this with the club when I am talking with them. That's what any serious manager interviewing for a job would do. It's not just "I have done this, this, and that, and this is my preferred system" but also "this is what I can do with what you currently have, this is what is needed to step up a level, and this is how long I think it will take." Don't forget that it's not just us that have to sell Spurs to JN; he too has to sell us on what
he can do. So all of the things you listed are really non-factors, if JN has done his due diligence, thinks he can take the club forward, and the club buys into what he is pitching.