Buying a house I can't afford? House hack?

[Andrew Leung]

26 years old, $150k salary, would be first-time home owner, $800k house

Wondering what you more savvy folks would do in this situation. A relative of mine is selling her $800k 5br single-family house in Merrifield area, walking distance to Mosaic District. I really love the house and area. They are able to successfully rent it for about $4k/month. 

They asked if I was interested in buying it from them, but I don't think I can afford it. I'm aware of that no more than 3x your income rule of thumb, but what if I was thinking of it being my first house hacking with FHA 3.5% down loan, living in 1, renting out 4 of the bedrooms? Is that any more feasible?

Any advice would be greatly appreciated!