So, I'm thinking of being the bank, and the collateral would be the property the borrower is buying. 

And I don't want to apply to a bunch of places and have them drop my credit score by inquiring too many times.I'm perfectly comfortable putting the townhouse up as collateral as well as the warehouse (the one owned in my personal name) too.

The interest accrued can be itemized in your 1040 If your primary residence was used as a collateral. 

You may have to put up one of the properties as collateral for the line of credit.

Each lender will be different and you will be treated differently based on your experience, collateral, and relationship with them. 

Business loan using both properties as collateral.3.

You'll have to essentially give them a couple hundred dollars as "collateral" and you're set.

Loans do tend not to happen by accident under tax law - the courts like to see notes, collateral, and a list of other "bank-like" arrangements for a vague transaction to be viewed as a loan.Contribution via a personal credit card buying something for the IRA.....muddies things up a bit. 

Do they care if you use a HELOC to purchase another property out of state, or does it make no difference to them since it is a collateralized loan? 

The higher down along with your father's backing shows better collateral if you will.I think you'll find that the more you talk about your goal on this site and others in person that opportunities will present themselves.