Either negotiate a good price or only pick upgrades that's necessary in the rough phase and do the upgrades with your own subcontractor/vendors after the house closes (kitchen upgrades, appliances, countertop upgrades, flooring upgrades, landscaping upgrades you can get them much cheaper without going through the builder).New construction is a winner if all things are the same. 

We come across a lot of owners super frustrated with their current manager and the main issue seems to be communication, on top of cleaning/maintenance and lack of attention to detail.

This tenant operates a resale business and is currently renting a single unit on the ground floor.

Personally, the last thing I would want to do is purchase a STR in a community where every neighbor is my competition and floor plans are similar if not the same.

We come across a lot of owners super frustrated with their current manager and the main issue seems to be communication, on top of cleaning/maintenance and lack of attention to detail. 

Purchased rentals that are all clean BRRRRs and now have a successful rental portfolio.

Is it possible to lower the window to the floor and install a tempered window?

I expect the project will be a bit cheaper than the quote because I've been sourcing materials myself which were included in the quote and was able to buy new hardwood flooring on fb marketplace as well as buying nice hardwood cabinets from Habitat Restore that will be refinished instead of buying new plus a few other fun thrifted finds to keep costs down!

In these instances, you'd have to check things like flooring, plumbing for leaks, roof for leaks, hot water heater, and heating and air conditioning units. 

Hire a Architect to provide drawings with a lot of details such as existing house elevations and floor plan, proposed elevations and new floor plan, roof, wood deck, addition, etc.