To be as apples-apples as possible, what sort of rent roll would you get with existing housing for that investment size? 

Depending on the size of your ad campaign it may make sense to do it yourself.

For a fee... you're looking at roughly 5-10% depending on the deal, the market, the size of the property...as every one will differ obviously and different companies have different policies, etc.

A bathtub full of water with a human in it, or a king-sized bed with two humans, isn't something they necessarily automatically make attics able to bear. 

There really aren't that many, depending on the size of the deal and structure of the complex.

I am house hacking in a medium sized town in the Northeast. 

If not, then a much easier solution would be to increase the size of your top unit by adding on.

@Kyle Brodwater, try Water Tech in Rehoboth, MA they have a web site where you can see the sizes of the dumpsters and their very inexpensive.

Depending on the NOI of this opportunity, $900,000 can get you into a considerable size mobile home park or other type of investment (I really only know MHs).

While our home is nicer than the recent sales, the appraiser would have to put us above anything that has sold recently for our size home.