I have gotten a seller's credit for my 3 existing units but to be conservative, I will assume I am paying full closing costs here.At the moment, I have ~$25k in a HYSA and expect to save another $10k from my W-2 before I start putting offers in.

Id go right into looking at local credit unions and small community banks for HELOCs (lines of credit) so you can have a lower blended rate and draw/payback as you please.For the 3F - Since this is free and clear, you would only be looking at 1st position options here in the world of financing.

They also have the Mortgage Tax Credit.

Credit unions, banks, mortgage companies and private lenders.They all had the same answer.

If the home is occupied, there's usually 1 group showing scheduled, so you'll want to come prepared with your comps and ARV. 

Several options you can explore to get the down payment capital: Solo401k; HELOC on personal residence or from equity of the SFR; Cash Value Life Insurance Policy; Business Credit; Private Lenders, to name a few.

Private lender will be close to a credit card interest rate for them to finance something like that.

Look at it more like a credit card.

Also consider contacting houses that look vacant, simply door knocking in a neighborhood that you are interested in and talking to the homeowners in a genuine way, For Sale By Owners is another potential, using an App like Nextdoor or Facebook pages/groups related to local real estate and just telling the group what you are looking for, contractors also know about houses coming on the market soon and so do property management companies, and finally garage sales are a good way to find off-market properties as people prepare to sell.To Your Success!

There’s definitely a strategy to applying for business credit to avoid alerting other lenders that you’re shopping for credit.