I am new to real estate investing, looking for my first project and wondering what the most accurate way is to run comps on properties.

Perhaps I am way off and your calculation is much more accurate. 

If you are using numbers that are guesses, or hopeful....then you wont get an accurate picture of what the true cash flow is.

Is that accurate?

How do I get an accurate value on what it is worth?

Also when I am trying to get quotes online, it only allows me to put the address in for one side, how do I accurately get a quote for the whole building?  

I understand this of course but I am wanting to learn the subtle ins and outs like what are the first things to look at on a property, how do you accurately calculate your costs (fixed, rehab etc) before someone else grabs the house and before you have the experience?

Propstream's information is more accurate and updated.

we get these weekly from our title companies   this is very accurate data and in real time. https://altos.re/r/f97cf59   I have a 90 home community starting in this city in 2 weeks  IE break ground for the streets and roads etc.so we like to keep a close eye on it.. then I know also what my competition is doing  IE Lennar and another larger regional builder.. 

Note back to #3, always have exit strategies to handle a variety of situations as they arise.I always like to keep the mindset that the money is made when you buy the property so always track your numbers closely to ensure it pens out when you buy, not a few years down the road based on a gamble.