noob question about adjusting comps

[Mike B.]

I'm currently looking to purchase my first home as my primary residence. I've been looking at single family homes in the Chicago suburbs, mostly 3 bed/1 bath ranches. Most of these are beat up REO's that are selling for $40K - $80K and have an ARV around $80K -$140K.

I'm struggling to figure out how to estimate the ARV. I'm not sure if I should pick 3 or 4 comps that are close to being exactly the same, or if I should pick like 10 or more comps that are similar and try to adjust the values for the differences in the homes.

I just don't understand how much certain features are worth. For example, I'm looking at a 3bd/1.5ba ranch right now with a 2 car detached garage. There are a lot of comps that are 3bd/1ba with a 1 car attached garage. Can I use these, or are they too different? I have no idea how much to adjust the price of mine because of the extra half bath and the garage differences. Also, if I find a 3bd/1ba ranch with a full basement, can I use a 3bd/1ba ranch without a basement as a comp? If yes, how much is the basement worth?

I have no idea how much a fireplace is worth, brick as opposed to siding, 1 car garage vs. 2 car garage, etc. And if I find a home that is 1,000 sq. ft., can I use a house that's 1,100 sq ft as a comp? 1,200?

Sorry for making yet another thread about comps. I couldn't find an "official dumb questions thread" to post this :) Thanks very much for any advice.