So how does this Brrrr thing work?

[Klaycon Santos]

I have a property i wanna purchase for $300000 (multi family) and it needs work. Watching videos about brrrr it gave me Hope's to tackle this. I have 50000 towards down payments but 0 towards rehab. How do you guys approach this? Would hard lender be an option? Bank is willing to fiance but I'm not waiting 2 years to refi. Should the property be vacated? Should I have a tenant stay so he can help keep paying rent for morgage? My strategy was to offer 10-20% below asking price and if accepted, I would move in a fix out what I can solo. Any advice good or bad I'll accept. Thank you.