It's a huge mistake because your increased tenant turnover and turnover costs will eat up your cash flow.

In my own home, I was in the process of a refi, but after the appraisal came back at $70,000 more,  I am backing out of it and eating the appraisal fees rather than the refi fees.

Also, you get taxed as a short term capital gain which eats up a ton of profits.

They eat up TONS of CPU and memory (64-bit Windows with 4GB RAM) and often cause the browser to lock up (Google Chrome - BP doesn't work right in IE11 anymore)....although, it's been educational using Windows Task Manager and watching how long it takes all the stub processes to run down after you close Chrome...

My Personal concern would be having ample cash reserves when you are done with the rehab.  2 units will eat cash on occasion, be ready.  

Doing this 100% financing eats up a lot of any profit and if you have no experience, you would have to contract a home run or even a grand slam deal for anyone to want to do it.

There are many other fun things not shown: Complete rewiring of all electrical, including new meter base and panel.Lots of attic and crawlspace work.Insulating walls, attic, basementAnd so many other random tasks that eat up hours and days, even though it seems like nothing at all is getting done. 

Some numbers for your perusal:Purchase price: 70kLand value plus shop 35kMoney this house could easily eat before all is said and done in fixing it $70KValue if we poured $70K into this house  $120-130K todayValue as-is  $55KRent the house could fetch if we dropped $5K into it  $800/moExisting mortgage $622/month pitiCould refinance to a piti of $500/monthI ran a scenario where, if I dropped $10k to stabilize the condition of the house and $25k to convert the garage to a studio apartment (rent for $300), it would be around 10 years before I could break even.Thanks for any advice or insight you can offer as you play the what-if game with me.

Not just in 'going' all over, but in damaging walls by 'eating' the drywall, being aggressive to neighbors, and overall disturbance to the building.  

Don't believe in words, let them eat it by writing it.