You should do all the due diligence you would as if you were going to be buying, fixing, flipping the property yourself with your own money - because if the borrower fails and you have to foreclose, this is what you will be doing.
Borrower should be paying the fees for appraisal, inspection, title policy for lender, and attorney's fees for drafting.
As an attorney, I drafted hundreds of doc sets for closings in Texas and the rest is specifically limited to practices in Texas.
In TX, my doc sets include a Warranty Deed with Vendor's Lien, promissory note, deed of trust (the lien instrument), lender's instructions to the title company, attorney letter of non-representation, and either 1) a personal guaranty (if an entity borrower) or 2) a business purpose affidavit (if borrower is/are individual(s)). There can be additional riders for certain situations.
Close at a title company/fee attorney office (depending on local custom).
As for early repayment killing ROI, you can have a minimum interest clause to guaranty yield. Rates and terms are a balance between local market and your goals.
As a business model, it takes a around $2-3M to make it a full-time adventure (depending on geographic and asset class restrictions). But overall, pick a niche and get very efficient at that.
If you take money from others to lend out, that becomes a security (a la, SEC and state regulators). That model can work too, you just have to comply with similar rules as syndications.