Since I am a numbers person, I like to look to be able to compare scenarios to help build my strategy, but I have found it difficult (even hired a wealth strategy consultant) and have not been able to find anyone to give me such examples and scenerios.

So if your plans differ significantly from what it was originally planned the infrastructure will need to be modified.You should asses the current condition, you can hire a civil engineer to go out and take a look at the pipes, stub out locations, grading, etc.

My only hiccup in the project was with the window company I hired to replace the old aluminum sliding windows. 

I plan to self manage, but ran the numbers as I were hiring out the management.

I have tried to hire four people in the last two months and they have all been no shows.

So, if the parties negotiate with each other, it is always an element of negotiations to say to the other party something along the lines of, "You might be right in what you are claiming that you owe me only $XX, but you will have to hire a lawyer to find out, so save the legal fees and pay me $XX plus $YY, and it will still be cheaper than paying the lawyers." 

If both parties agree on terms (price, etc), you could always hire a RE attorney to go over with and explain the contract to the seller before he or she signs for probably a 1/2-1 hour consultation.

In 1988 I quit my job, started a consulting company, hired people, etc., etc. 

In this case I would be hiring people to do the work on the house instead of myself as it can get done quicker and I won’t get burnt on working on it every day after work.

Other option is to hire a lawyer to lobby for you, but that will be an expense, and the path of least resistance is to gain favor with the neighbor and council person.