Deductible: This is not a coverage but rather your portion of a claim.

The HELOC monthly interest would currently be $1,300 per monthly (potentially tax deductible) versus the $1,800 net monthly cashflow from the 9 additional properties at $200 / month / each.

I was wondering if this is eligible as a business expense - or another type of qualifying deduction - so that I could finish up my income taxes. 

Hello,When using a HELOC to purchase another property is the interest not tax-deductible? 

Can I deduct those $10k on my 2020 Federal Tax return?  

I assume you mean income tax - I would suggest getting help from a CPA or a good bookkeeper, as you will have other deductions too - like depreciation, interest expenses, etc etc etc   - but for the mortgage, your interest is the expense. not the principal. 

Losses on the other hand can be currently harvested to benefit from the loss deduction.

Will the bill meet your deductible?   

If you aren't already, I would start with your TSP to get the tax deductions and the match.

If you're allowed to deduct this loss, it will reduce your overall tax.