We agreed to the following modified terms:10% of monthly rent, which would be $90 assuming it rents for $900. 1/2 of first months rent for finding tenant, which would be $450 assuming it rents for $900

Don't be so desperate to get a house under contract that you modify your numbers.

Your state may or may not follow the UCC in its entirety, or may even have case law that modifies these rules.

Have a contract on 2 lots on a cul-de-sac - since I had posted about this most of the lots are gone - another contact I have met through BP may buy some of the remaining ones and we were going to see if we could combine forces in some way.Met with the draftsman today to finalize the designs - he has an off the shelf one he's used over the years for some other large duplex builders over the years he'll modify for us.  

Changing a neighborhood: You can "modify". 

I'd like to own 1 within a year, 3 within 2 years, and 10 within 5 years (disclaimer: that's a first pass at setting some goals, so I reserve the right to modify).

"local cost category modifier"= category a: (+10) + category b (-10) + category c (+10)/ 3.

My plan as of now is to pull a general purchase agreement from the internet and modify it for my type of transactions.

Or did you take the standard GHAR and just modify it?

For date changes most payment services should be able to handle this as with our service we can modify a particular automatic payment to run later for just that month and include late fees, if necessary.