Hi everyone, I have been looking around a while in Decatur Alabama to buy multi-family (5 units and up) properties because it seems there are bargains still available there compared to Huntsville but there are some pockets where crime is really high.

You should be able to get all of the comparable information this person is asking for from your realtor, and your realtor should have provided this info to you already anyways so you can know if you are getting a "deal" or not. 

Maybe the same one...We'll have to compare notes!!

Rent for this house I’m buying will be in the $2800-3000/mo range, but there are some comparable rentals in the neighborhood that go for $3400-3500.

Even in the best case scenario, the ROI does not justify the large capital investment and relative lack of liquidity as compared to my stock portfolio (where I have more knowledge & risk tolerance, even in volatile markets). 

There isn't a whole lot of rentals in this area but rents go from $2,300 to $2600 for comparable properties.

Do you believe that a house that will be 100 sqft feet bigger than the largest comp and also include a two car garage is capable of selling at or above the highest comparable? 

They are appraised using comparable sales. 5+ units will take income into account

I cannot find any comparable properties with with to compare.

The biggest reason for me coming to America is that real estate here, comparing to Israel, is more beneficial and less complicated.