Deck might add some value and would advise to get a permit if you are increasing opening size and I would definitely get a permit if the deck is raised to the level of the current step  landing.

That would put the bank at a lower LTV and they might lighten up on their requirements.

Contact banks and see what additional loans they can offer with lower down. 

It is a full basement stacked tri-plex is a design with 5 bedrooms on each level plus a Mother-in-law style suite on two levels next to the attached garage and with a 2 bed/2bath ADU over a detached garage. (21 rooms, 25 bathrooms). 

I’ve been looking at areas like Newark, NJ and Philadelphia, PA , which I find attractive due to lower property prices and property taxes.

You may be able to get a cheaper loan, or one with a lower down payment. 

You’ll be near the lower end of that if you do 15 year vs 30

Also, if you plan to house-hack your property you may be potentially qualified to get FHA financing which is much lower than a typical down-payment of 20%.

Actual return is going to be much lower than pro forma return on rents that low.

Are you asking if you can sell the note with a lower interest rate of 5% to 10%?