However if you don't have the capital to do this, mailing is an okay way to start just don't expect to get a deal from your first 1-5 mailings.

Will they be actively involved in the deal as well or are they just bringing part of the equity and putting it in your hands with an expectation of a financial return?

If your score is, let's say, 775 in Credit Karma, you can expect your score in the report run by a lender to be 25-35 points lower (or more strict), like 740. 

If your managing your business you should expect nothing less than market rent.

Sure, I have some expectations that were not met, but those expectations were set because of my previous experience as a contractor, the research I had done and the experience of those who have gone before me.

I'm about 7 days away from closing on my first real estate deal and the thought occurred to me that instead of wasting time (and closing costs) dealing with a bank for the initial loan, I could simply use myself as the source of "private money" for the entire purchase (~40k) for a home that I intend to rehab.The rehab is expected to take 3-4 weeks and I already have a reputable contractor with a written estimate in hand and the cost will be a ~25k additional (worst case) on top of that.  

With Institutional money expect around 50% with 1st liens.

I’m not sure how plumbing venting works in these houses.Likely will also need new furnace and AC.Will need basic exterior remodel such as stucco over the existing brick .Finally it will need all the cosmetic stuff done like upgraded kitchen, bathrooms, floors etc.The house is 2900 sq ft but about 1000 Sq feet of that is the dining room and living room which needs very little done to it.Any rough ballparks on what I can expect this to cost with high end finishings?

From the sounds of your post though you are expecting to make lots of offers.

You can let them know what your credit score is and they can advise you want to expect with different loan options.