Would suggest using AIA A105 Standard Form of Agreement Between Owner and Contractor as a template for your contract.

The NWMLS PSA used here in WA has a standard Method of Payment Addendum that will address the details of a wrap or regular seller carry.  

Keeping in mind this can vary widely: I would say seller financed interest rates would generally be above standard bank rates yet lower than hard money.That is the question asked.

Also, its pretty standard around my neck of the woods to provide a fridge. 

. $800-$1,200 per month would be a standard range based on my experience for a rural-moderately developed area. 7% annual escalation on the other hand is more than twice what I would have expected, are you sure it isn't per Term? 

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.)