How to qualify for a new mortgage when keeping my house as new mid-term rental

[Clint Wenk]

Hope to find some help from the Bigger Pockets community!

I have some questions about qualifying for another mortgage when I have outstanding mortgages on investment properties.

So here's the scenario:

I am purchasing a Quadplex on 6/28/2024 and it's new construction. It will take a couple months to fill it with tenants. The mortgage will be for

approximately 900k at 4.25% and in my name. I have an LLC that I just created that I plan to move that property into.

I am currently living in a 3/2 valued at $600k with an outstanding mortgage of $300k. I would like to retain this house and turn it into a

mid-term or long-term furnished rental.

I would like to move out of that house and into a bigger primary residence which would likely be a $750-850k purchase price. I can bring 200-300k in down payment to that closing. I would like to have a mortgage payment in the $3500-$5000 range.

I am just getting started in real estate investment properties and don't know enough about how other landlords show that the other mortgages are covered by rents and qualify for additional loans?

I suspect that until I get both investment properties fully leased that my debt to income ratio will be too high.  If I can show the signed leases, is that enough evidence for a lender?

I have found a property that I like for my new primary residence and I am trying to see if the seller is open to a longer duration close where I rent from the seller for 90-120 days to allow enough time for the investment properties to get leased.

I am also considering asking if they would be willing to explore a seller-financed option but I don't know how to structure that so that a regular seller might find that more attractive than a regular closing.  I would be interested in talking to anyone that has structured some owner financed deals to understand how to approach that with the seller.

thanks,
Clint