I have a couple of short term first trust deeds ready to mature and need to re-deploy this capital.

You only need a place to track tenant information, payment history, maintenance, etc.

You inflated the price $70k but they are only making $50k in payments.

Look on the deed of trust, who is the trustee?

Maintain a credit score of 620 or higher, save for a down payment, and research markets carefully.

I get paid within a day of arrival (I now set up direct pay so I will handle my own payments going forward).  

You share the lease, you share his payment history, and you give a total of what is owed.

The website 51west.properties also scores low on scam advisor ("owner is using a service to hide their identity, high number of suspicious websites on the server, registrar has a high % of spammers and fraud sites, website is (very) young, website appears to be hosted by a company with a bad reputation", all according to https://www.scamadviser.com/check-website/51west.properties...)Trust your instincts. 

My current monthly mortgage payment plus projected future mortgage payment (2900+2900 = 5800).

They typically have multiple origination points (meaning very high closing costs) very high rates (compared to conventional but also compared to 6 month or longer waiting period DSCR products) and almost always have VERY long pre-payment periods up to 5 years.