Include the date, duration, and a brief summary of what was discussed (e.g., "Discussed renovation plans with GC for STR property").

I've heard of mentees who started cleaning up construction areas on a flip at the end of each work day or picking up supplies at Home Depot and delivering them to the job site.

I seriously thought the op date would be 2019, or 2015. 

I tried to google but could only find vacantion-like sites with exorbitant prices.- Is there a kind of person who could help me with pre-sale improvements (roughly saying, to tell me what is worth replacing, improving, etc and what is not,1 to make the house more attractive for the buyer)?

Is looking online at sites like LoopNet sufficient? 

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. 

Consider the ones that paid $20k - $40k on their credit cards for the full mentorships, spent thousands more on data sites, thousands more still on direct mail, email blasts, then even more on SEO and SEM.  

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