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

I agree local banks and credit unions will be better if you're planning on growing your portfolio. 

For a cash out refi, you are generally limited to 75% LTV and rates right now are in the mid 7s for good credit and a DSCR over 1.0. 

And don’t sleep on local banks or credit unions—they sometimes offer flexible portfolio loans that could work for a deal like this.Since your wife qualifies as a first-time homebuyer, check out any state-specific programs or HUD options for down payment assistance.

The neighbor was the hottest in the twin cities and this house has 83 businesses cards of realtors who showed the property.

No reason stated I had great credit score cash on hand excellent properties.

If you had good credit (670-730 range), you have 20% to make a down payment, and sufficient income to qualify for the home you want to purchase - Would you choose the FIRST-TIME HOME BUYER or CONVENTIONAL purchase option...which would you pick and WHY?

A proper vetting process - background, employment, credit, and reference checks - will weed out 99% of problem tenants. 

You could also get a line of credit for about $150k (you should be able to borrow 75% of the value.)The reason I suggest this is…1) you save $40-$60k in selling costs. 2) you have a lower blended interest rate (2/3rds at 3.25% and 1/3rd at 7 or 8% instead of the whole $500k at 7 or 8%) saving you another $1k/mo in interest. 3) you only pay interest on that $150k when you actually use it, not from day 1  Unless you hate this property, or want to buy something you can’t afford without selling, that would be my plan.

I'm not an loan officer, but I know some banks locally like ORNL Credit Union have offered a 0% down conventional loan product.