This is going to depend on your risk tolerance and preferences, but I'm happy to provide my input..If I were in your shoes, I'd do the HELOC because of your interest in BRRRR. if you were trying to do a long term rental, I would do a cash-out refi on your primary residence. 8 years is a long time to wait to do 1 deal, so I would personally shy away from depending solely on cash flow.

Longer term goal is to figure out how to make real estate investing my primary post military income source so that I can focus plenty of time on foster care and a non-profit we are involved with. 

There are lots of military towns where the base is the main source of employment (Lawton, Oklahoma for example). 

I do not know what average rents have done in your market over the last 10 years, but in my market (San Diego) the average rent has gone up ~1K/month in the last 10 years (source RentCafe). 

What data sources do you use to pull marketing lists to mail to multifamily property owners?

I don't know where they source their data from, but it's certainly not just folks that send them business. 

The Days on Market (DOM) figure for single-family homes fell from 51 to 26;Total property sales rose 9.2 percent with 12,036 units sold;Total dollar volume increased 26.7 percent to $4.3 billion;The single-family average price increased 14.0 percent to $380,233; The single-family median price rose 15.2 percent to $310,000; Single-family homes months of inventory registered a 1.9-months supply, down from 2.6 months year-over-year and below the national inventory of 2.6 months;On a year-to-date basis, single-family homes sales are running 17.4 percent ahead of 2020’s record pace.Townhome/condominium sales jumped 27.1 percent with the average price up 9.5 percent to $237,473 and the median price up 14.3 percent to $200,000;Single-family home rentals fell 10.2 percent with the average rent up 9.6 percent to $2,153; Townhome/condominium leases rose 1.8 percent with the average rent up 6.9 percent to $1,765.Source HAR

Total new listings entered for all property types in YTD 2021 was 86,787 vs. 83,247 new listings entered for all property types in YTD 2020.Source: FMLS

The club has had a lot of representation from companies like Cushman & Wakefield or Blackstone to a successful sole proprietor investor.

Or another source of assistance?