Yes, if you provide the supplies/materials for your work, you should definitely write them off as an expense.

For business code, just use 999999. It's a catch all for "other" businesses. 

Would you deduct the chemicals in the supplies category?

Yes, your chemicals would be a supply expense.  

I would not use 999999 as your business code.  That can cause a red flag during processing.  I would use 811490 - Other personal & household goods repair & maintenance.