You can check out sites like Zillow or Redfin to see what houses are selling for and what rental prices look like in your chosen market. 

Looks like a pretty straightforward site with comprehensive background check

Besides land, infrastructure/site work, and the building construction itself, am I missing any other major category of costs?

This is what I did for a cabin I built in Gatlinburg:  We took a few royalty-free photos of the area off of the internet, and submitted them to an art site online whereby they make a painting of the photo.  

It's not perfect, but I like to read the reviews from residents on the site 

I watched my parents flip houses since I was little and have always been on job sites or made "pocket money" by doing chores like painting fences or washing kitchen cabinets, which I realize now my parents were putting us to work to build that sweat equity.

Hello everyone,I was wondering what everyone thought on the 2 sites: Propstream and Propwire? 

At the end of the day vet these lead gen sites/companies on a short-term basis, then flip to something else if the leads are not working while having the right expectations.

With the wealth of information available on BiggerPockets and numerous other sites and books, I'm not sure where to start.

You will be too detached.5 is required in some states and not in others so a lot if left to your viewing on-site so if you are not seeing it in person, you need full photos and videos of every part of the basement and attic so you have an idea of where the trouble lies before making an offer.