I recognize this as standard business practice and don't see why you can't do the same.

IS THIS STANDARD?

use a standard NJ realtor contract. you can google it. if you are going to wholesale or assign the contract you just need to cross out the paragraph that says "not assignable" 

Is it common to have a standard amount for selling and buying costs?

It can be tough to swap out fixtures while residents are living there, but when a resident moves out, I'd recommend an ultra high-efficiency toilet(the Niagara Stealth at Home Depot uses only .8 gallons per flush, half as much as a standard toilet and about 38% less than what is considered a high-efficiency toilet.)

Another point is that a FHA /VA loan will cover up to the  4plex with  specific criteria that you have to at  least  live I  it for a certain amount of time -  generally a year is the  standard.  

Doing this strategy on your own properties is much safer and a profitable alternative to the standard rental.

Your only out is to either evict them on legitimate grounds or, when their lease is up, you explain that they need to reapply to meet your basic standards to move into the unit.

So does anyone know what the standard sets of documents that I should request?

I have no idea about PA so I will give the standard answer, contact a local attorney or one that is more familiar with the laws of your state.