Partial sale of property where my home is located

I have lived in my home on 5.25 acres for over 25 years. I recently divided and sold the back portion of my property. I am owner financing to be paid off within a year. I am not sure how to go about using the original costs of the property - example

Purchased property 40,000

Fenced entire property 30,000

Land clearing ect 60,000

 

Can I take half of what i spent on the original 5.25 acres and write it off for selling half of the property - so write off half of the purchase, fence and land clearing? Then use the other half to write off when and if I ever sell the portion with the house on it?

Also I am owner financing at 0% interest as they are paying it off so fast - how would that work with the IRS for taxes as there is not interest.

 

Thank you