That's missing the forest for the trees, but you do need to manage cash flow because if you're buying conventional you'll come across DTI issues soon and if you're buying nonQM it needs to be 1:1 ratio at minimum to be qualified without unfavorable terms. 

Borrowers in certain states or with high credit scores may qualify for  80% cash-out , but it’s important to weigh the pros and cons.

Quote from @Roy Lam: They only qualified for two bedrooms voucher, but i have a three bedrooms  singles house. 

(It's funny now) I hired a property management company and sure enough they told me the best qualified renter was the one who wanted to do a 9 month lease and pay it all upfront.

Sponsor quality far surpasses the "deal", assuming a qualifying criteria for a "good sponsor" is that they don't buy crappy real estate deals to begin with.Having said that, if a great sponsor is offering a deal you don't like for some reason, don't invest in it--just wait for the next one. 

If you plan on purchasing your new property with a loan based on DTI, then it may be harder to qualify if you are leveraging yourself some more.

Most serious and qualified tenants are searching on the major 3rd party platforms you mentioned + realtor.com, redfin, and a few others.Apartments.com & homes.com are owned by the same company and may offer some additional marketing options.Another strategy to consider here is social media - video marketing.

You cannot use rental income above your mortgage payment to help qualify for a larger mortgage, but you can utilize 100% of the lease income to offset so that should help you qualify for more of a mortgage. 

Marie Johnson That has to be bought by a qualified non profit organization, and is only allowed by certain investors/lenders.

Interest rates and points are not the only criteria upon which to base a decision; length of loan, amortization and if you can get it “loan assumability” especially with no qualifying and no rate escalation could e much more important.