I'm going off the understanding that you still need to spend 500+ hours in the business to achieve material participation (please correct me if I'm wrong). 

In the latter case, I would still use QB to enter info provided by the 3P servicer and to maintain my general ledger for the lending business.

I am seeking advice of what to do with the money from someone who exit the business and successfully got similar income and appreciation of capital.

Several options you can explore to get the down payment capital: Solo401k; HELOC on personal residence or from equity of the SFR; Cash Value Life Insurance Policy; Business Credit; Private Lenders, to name a few.

Real estate investors are sitting on an untapped goldmine of financial leverage through EIN Corporate Credit, a strategic tool many overlook.

I'm wondering if a BLOC could help to build my business credit.

PMs and realtors want to use people they know that have been in the business and do a good job for them.

Quote from @Francisco Solano: I suggest you ask a business attorney in your state for this basic template.

I’d recommend starting with business credit cards that only require a soft inquiry, so you don’t risk a denial from one bank that could influence the others.

Also are you doing credit checks through them?