I mistyped as 250k sorry its 225k and it has an z- estimate around $1495 per month (however realtor is telling it will rent from $1600 -$1800)  ..for the 150k one, I see similar place with current renting list price is $1295.Which one do you think is best option?

Double your estimate for time spent on the painting and flooring and you'll be close to real time spent.  

Thank you very much for providing a detailed estimate to double check my numbers.

I had the inspection and estimate done this weekend, and it is about $15,000 higher than I originally ball-parked on my walk-though estimate.My question is: if I offer to remove the Contingency only if the Seller agrees to a sale price of $155,000, how likely are they to accept it? 

Since your looking to accumulate a portfolio in the USA you may wish to research forming a corporation or LLC in one of the business friendly states.

Scott The Book on Flipping Houses, The Book on Estimating ReHab Costs http://www.biggerpockets.com/flippingbookTo find out about an area go to IREM.org search for ARM certified property managers.

I realize that the rent number doesn't relate directly to ARV, but when doing a gross estimate, if I can buy a property, say at $120k that has an ARV/market value of $200k, do I look to the lower end or higher end when using the guideline?

Along with getting the house under contract you need to know what the seller is willing to sell their house for, and consider what they need as well as have the opportunity to evaluate the house and walk through it to estimate repairs if needed.

Also, $/sq ft construction estimates have increased significantly in my area in the last year.

Now that I officially know about the mold, I may have to pay about $20K (2 estimates so far) to clean it up, taking it back to the studs in some places, pulling back the baseboards in others, then cleaning with sporicide and doing air scrubbing in order to get an official clean bill of health since i can't rent or sell without that, having officially established that I have mold.