I can lock in my debt rate for 10,12,15 or 35 years on apartments (can't do that on other asset classes).Keep an eye on the spread between the 10yr treasury bond and the general cap rates for say multifamily.

Even if you never buy another property and just slowly pay down your existing debt (or not) the benefits of rental appreciation alone will take care of you.  

At one lender, he indicated that my debt-to-income ratio is too high, since I currently have three loans (primary residence and two investment properties, one of which I'd sell and 1031).My income is fairly high, and due to a job change, it's recently increased $20k. 

AKA the actual rate of return on a property you are feeding will generally be poor and you would be better off with a better cash flowing rental or in the stock market.Of course, if you found a great appreciating market or structured the debt to be shorter term, feeding a rental could work out well.

We have built business credit through Unsecured working capital such as a business  credit cards, lines of credit, and small business loans. 

Home equity lines of credit and credit cards.

If not what are you figuring for debt service?

They will look for experience though, as well as your debt to income ratio, W-2 income, and any other assets you may have. 

How much and what kind of debt do I have?

@Eric P.We let our guests know that we accept direct bookings in several ways: post-stay text and email follow-up, post cards and business cards displayed in all our properties, giving each property a unique name and promoting it on social media and elsewhere so guests can do a quick Google search on our property name and we appear everywhere.Increasingly, we are seeing even some first-time guests seeing our property name on the big listing sites, then finding us with a Google search and booking directly on their first stay.