Since you'll be living in one of the units, you can qualify for owner-occupied loans, which often have lower down payment requirements and interest rates compared to traditional investment loans​

Cash up front would be a bigger requirement for STRs too so it's not a "cash-flow" method, it's just your moving cash around differently.

I am a first time real estate investor looking the following property : https://www.redfin.com/OR/Forest-Grove/2418-Cedar-Cir-97116/...its a pretty large duplex in Forest Grove OR,  the trick is though, its on a lot zoned for a 4 plex so I am lookinginto house hacking, converting into a triplex, then living in one unit while renting out the remaining two unitsThe left garage has been converted to living space, with a living room, half bath, a laundry room with a sink and some counters/cupboards and a bedroom, it is a part of what was an existing 3bd unitIf I were to acquire the asset, I would first attempt to convert that space into its own unit The line items as I see (be in mind, I am totally new to this) would be to >put up dry wall where the door to the rest of the house is,>add a shower to the half bathroom >install a water heater in the adjacent 3bd unit> install a kitchen in the laundry room, (stove , oven , sink, counter space)>add a shower to the half bath Assuming I can convert it to a 3plex, I could at-least cash flow on my investment after I leave My plan would be to put minimum down payment of 3.5% (FHA loan) that way I can have a decent amount of capital free to do the renovationsThe only concern is when I crunch the numbers to get my ROI, I have no idea how much its going to cost to convert the additional living space to a third unitAny experienced investors here know how I can estimate this before I try to make an offer?

As per the article from CAS below, it does require disclosure.

It might mean you can consider slightly higher purchase prices or invest in properties that require more rehab.

Buyers: How do you feel about the requirement for written agreements before seeing homes?

I earn much higher returns than I ever did as a rental investor, with almost no work required on my part.

Electricity, water, property insurance while you own the house... that could be a couple of thousand dollars.  

It's a B- class neighborhood.Apparently there is some dog pee odor and some bad scratches in 2 of the 3 bedrooms and water damaged next to the kitchen (which is tile).The bamboo flooring flows through all the rest of the house except the bathrooms and kitchens.Would would you suggest?

Cash flow for businesses require more time which usually means higher returns in $ amount, % of CoC Return is more difficult, and keep in mind your time. my rental takes a hour a month and maybe cash flows $100, $100/hour is nice, but took $60k.