I know that house prices are inflated here much like the rest or the country but it also seems rents are low. 

At the very least, you can consult with them and ask about their services and what the state requires to get an idea of what you would need to do without hiring them.  

Buyer pays $40k down, and the rest will be paid via sellers financing at 5% interest on a 10 year note, 20 year amortizations with a balloon payment at the end.Is it correct to assume that:1.

I have always had 80-90% of my total net worth invested in real estate and the rest liquid as a cash reserve besides maxing out my IRA, SEP IRA or Solo 401k for tax purposes.

It would take a 4.5% ROI just to cover your admin costs and break even.You could look at simply opening a self-directed IRA with a low fee custodian like IRA Services Trust Co in the Bay Area or Kingdom Trust Co in KY. 

My question is: is using the rest of the HELCO money as down payments on cash flowing rentals a good strategy?

Apologies shift blame to youYes this business can be built off customer service and good tenant relationships.... treat people with respect and dignity....don't be an a-hole.

We have used two different ones and both have horrendous customer service, less than qualified contractors and inflated costs. 

Any skiptracing service should be able to help you out.

Strategy is to approach «mom & pop» sellers of multifamily, distressed properties with some sort of a problem, 10-25 % seller financing, rest bank loan, reposition the property after problem solved,refinance well, manage well and repeat process.