Rent payments were being made prior.

If the seller's contract lists a deposit that was never paid the tenants must execute a Certificate of Estoppel prior to you closing which states no deposit.

I've read in a book that Real Estate Investment in Japan is often referred to as a "Scientific Investment" because it can be managed with profitability that is close to the simulation of earnings based on prior calculations of yields.

Yes for example we have (depending on loan) min. 6-9 months required. so even if they sell it prior they still pay interest for that period.

I also grew up in Cupertino and lived in Palo Alto Napa valley prior to Oregon..

What should be some things I need to be aware of and consider prior to signing any sort of contracts?

You mentioned Schwab, so I went down a brokerage track with my prior response.  

Landlords in NJ are required to have their rental properties built prior to 1978 inspected for lead based paint  by July 22, 2024 per a Phil Murphy signed law in 2021. 

I see former players from the 2000's coming back to the industry under different business names, and some of their prior work was less than stellar.

I will get all of these fixed prior to renting, not going to put anyone, including myself in a potential liability situation.