Any tips on rehab- first timer

[Monica Davies]

My strategy is buy and hold.

I'm owner occupying my first property, a duplex with my half of the basement unfinished. It's currently 2-bed, one bath with nothing sheet-rocked and barely framed downstairs. I want to add 2 bedrooms and a bathroom downstairs, and I'm estimating (but not confident) I could raise the rent from 950 to 1400. It's a 40 year old property, so the duct work, electrical, plumbing is outdated and weird, and I'll have to make the windows larger to be up to code for a bedroom -including cutting through the concrete and digging bigger window wells. 

I'm planning to refinance after I get this project done, I've owned the property a 1.5 years, and I think with our crazy market, the gained equity should re-coup everything I'm investing in the rehab.

I've never rehabbed before, and I'm getting bids between 20-30K for general contractors. 

My questions are: 

-I get an extra $450 a month, X12 / 30K, that's an 18% cash on cash return, right? Is that worth it?

-For anyone in a similar market, (I'm in Utah Valley, Utah) are my estimated rent numbers even close for a 2 bed/1 bath vs 4 bed/2 bath ?

-And any tips for picking the right contractor?