As many of you probably know (and I just learned), proof of a consistent flow of income from the same employer for 2+ years is extremely important when it comes to receiving a loan (regardless of my excellent credit score and lack of debt). 

@Brandon CraigHi Brandon I'm going to be the first response here and the 'wet noodle' of sorts.Firstly, get your credit working for you. 

You should then receive a physical collateral file if not already an electronic one - Collateral file is a a file which contains all of the previous mortgage paper work including things like alonges, deeds, borrower personal information such as bank accounts and credit scores at the time of the sale, pretty much all the paperwork submitted, required at the time of the sale. 

There's many independent banks and credit unions in my area who no longer even write mortgages, they just refer their clients to big banks.

Credit/debt isn't really a huge issue, it's more our comfort level.

Something that also does online applications and credit checks etc?

If you want to do more prep work, another BP user has offered House Flipping Spreadsheet which is one of the most straightforward and affordable estimators I've seen.But give your buyers some credit. 

I play along when cold called by the refi call center guys, probably get my credit run once every 3 months while playing along.

The SDIRA is responsible for all credits and debits incurred by the investment. 

But I recall Fannie Mae backed loans having a base DTI of 36% and it can go up to 45% if you meet credit score and reserve requirements.