Going in with practically no down payment, what is the best way for me to gauge how profitable my investment will be?

It might give some flexibility should, for some reason, you want to foreclose later....other liens to wipe out, quirks in the local laws, etc.

This is my first question on the forum so I hope I'm adding it to the right category…I am partnering with my brother in law in purchasing and building a vacation rental house.

He was there and said I should evict him, he wasn't leaving, and he knows the laws and if I want him to leave I should give him is deposit back.

There are some things realtors can't give opinions on due to anti housing discrimination laws, but any agent worth their salt should be able to provide you with rental comps from the MLS

I have found it harder to find someone to build a four-plex because ADA laws come into play.

@Logan Allec provided an outstanding explanation, and @Basit Siddiqi added couple good points.I just want to frame the bigger picture: the new law does NOT hurt ("hose", using your word) people who receive 1099-G for prior overpayment. 

In practice, I think a lot of people for an incidental expense just throw it all into one property.

Again, the lender is going to be a big factor in determining what you can do within the limits of the local law.

I don't know what took me so long to get on here...I am an CA licensed attorney practicing real estate law, estate planning, and immigration law.