I believe most people who use this site have been in your position.

The site was under construction and I only recently got a login to the site.

Should I see what Realtor, Redfin and other sites list similar properties to get my target rental rate?

I used to post here a lot back in the day, and boy the site has changed..  

It presents a rare opportunity to activate an iconic site with both community impact and scalable economic returns.Currently in the planning phase-focused on gathering resident insight, cultivating brand partners, and aligning with forward-thinking investors and civic stakeholders ready to help shape a legacy project rooted in culture, commerce, and change.Due to the unique nature of this concept, additional project details may be shared upon request and may require a mutual non-disclosure agreement (NDA).

The 203(k) loan is a bit more strict with respect to DIY that you might think.

I've seen that it can cost 500(diy, risky) to 5k(formal, costly, safer) but I don't actually know what I can get from it at this point. 

All this information is available on SEC EDGAR site

As for how they know they’re getting a good deal, some of these sites that allow you to list your tradelines and match you up with renters/borrowers (or however you wanna refer to them) will list out the details of the tradeline that matter such as how long the credit line’s been open, the credit limit, balance on the card and your credit score.

That will syndicate to sites like Zillow, etc.