I would discuss financials on this if you choose to come see the pre-rehab on Dec 1 (I have made a lot of money (close to 7 digits after this rehab is done in ~2 months) but due to not executing a cash out refi (due to the rate increases) my return is below my underwriting).

You are required to file a complete and accurate return, which means reporting the income that you earned along with atleast the direct expenses that you incurred on your rental.There are two comflicting forces - Your tax accountant wants to be aggressive with deductions because it will entitle you to paying less taxes(now or in the future).Your lender wants to see as much income as that will increase your Debt to Income Ratio(DTI).The good thing is that you can speak with your lender about 'one time expenses', that were only incurred in that year and are not reoccuring. 

For both the applicant(s) and a co-signer, you want to understand their habits...financial, employment, legal, character, etc., as Bad habits in one area typically carry over to other areas, and will land you a poor Tenant (or co-signer) choice.

Are you debt averse or want to take on more debt?

Prioritize your financial stability.

Quote from @Tim Johnson: Has anyone seen an example of a lender combining debt with equity on a real estate deal?

They are either going to be financially strapped or leave the area, or both.

I always tell my clients to put a reminder on their phone to go off monthly to ensure they pay off all debts like this that can cause them to have higher credit scores. 

A triplex or quadplex could provide more units for rental income, but obviously will require more financing, so having your financials and pre-approval lined up early is key.Since you’re already looking to network, attending local real estate meetups is a great idea—you can also connect with seasoned investors or agents specializing in Long Island properties who can offer advice specific to the area. 

@Zach RumfieldI agree with @Bill B. and @Bruce Woodruff that, financially, this is probably a no brainer and that you should run the numbers to see how it pencils out because, even though your dad already owns the property, there are likely still some upfront costs to consider.1.