Banks and even Hard Money will want you to have some skin in the game.

So I could earn extra return and 2. so I'd have additional skin in the game).  

If they require borrower to have 10% skin in the game or a net worth equal to the loan amount and you don't meet either of those requirements, be transparent with the bank.

I've read the forums on how to do pre-screenings, but I think most DC landlords are not as rigorous and I think people may be irritated by having to fill out the screening form before a showing.

We normally figure $6K for closing costs here in MA.The only risk to these I know of is that sellers might decline your offer because you have very little skin in the game.  

You are putting up $20k cash, he bears the financial risk if the deal goes south...all else equal, I'd say a fair profit split would be 70/30 or 60/40 in your favor since you have skin in the game and his risk is contingent.

OMG this is the most irritating thing in my entire life.

Being close to the mean is good; getting a rental on a street with too few rentals can irritate the owner occupants ("we don't like rentals" mindset); on streets that are close to 100% rentals you will find that some of the landlords don't care, and it shows in the tenant quality in some of the units there (and that can drive away the better tenants).

I expect that most retail stores automatically mark things up by a few percentage points to cover the expected use of credit cards.On a $100,000 project, I would think that most people would be irritated if I automatically added $3k to the job assuming they'd pay with a card...

A third aspect to look at: The net effect of what you're actually paying.... investing skin deep Mortgage insurance in 2014 is no longer deductible (consult a tax pro) so if you pay monthly MI and you'll have to use after tax dollars on this expense of owning a home which may dramatically increase the cost of borrowing.