I've talked with architects and contractors and have gotten either a lot of friction or >100k estimates to add a bathroom/kitchenette to a detached garage. 

If so, around how much (an estimate) is a typical startup cost to complete a full downstairs of a home for airbnb while istay upstairs to myself?

The $2k is definitely a conservative estimate for rent.

I’m looking just for a ruff estimate with the down payment, closing costs, and small rehab and emergency funds how much would you guys feel safe with to start looking?!

Where some of the flippers I have helped went off the rails occasionally is under estimating the rehab costs.

This is provided you realistically estimate and go towards cash flow. 

Here are the numbers:Location: San Fernando Valley (Los Angeles)2bd/1ba - 850sq ftRemaining balance: 314,000Zillow estimate: 676,400Redfin estimate: 713,749Rent Zestimate (Zillow): 2771 (I feel this is a tad high for such a small house)Cons of the house:Old roof mounted package unit, that eventually will need replacing (made in 1999)Still need to repair 4 sides of fencing repaired/replacedDriveway needs a slurry job1 hour drive from my current house with no trafficLawn needs a redesign (more drought tolerant stuff) - It gets very hot in the valleyPros:Mortgage is only 1760 all inPotential ~900 net/moI already have it...If I did sell it, I would like to buy something closer to where I live, but I also don't want to get dinged with any unnecessary taxes either. 

If it sells for what it is currently estimated at, we would both be debt free (or close to it).

The 8 month rehab estimate came from info I was able to directly garner from speaking with my buddy Choby's own licensed contractor who has worked on several of Choby's personal properties similar to this one.

The key to success on these deals it o accurately estimate your rehab budget and the time it will take to get the rehab done.