We sold it after 3 years as the appreciation was so significant, it would have been foolish to hold it longer and roll the dice.  

Any ideas on what to do here? 

Both properties have a substantial amount of equity that’s essentially sitting idle.Would it be a good idea to tap into this equity (through a HELOC, cash-out refinance, etc.) to fund future fix-and-flip projects or purchase additional rental properties?

Current individual stock portfolio (non-retirement accounts) with holdings that might be volatile in the next few years (big tech & big oil). $51k is about 17% of the portfolio and gains on the stock holdings are already 100-200% (long-term).

The brokerage house can lend on margin for securities they hold. 

I wouldn't let the idea of purchasing a home that has oil heat deter you. 

I live in the Tyler, TX area, but I hold my mortgage licenses in Pennsylvania and Texas.

If a landlord plans to hold the property for a while, we always recommend an annual lease, ending to align with the summer leading lesson, or staggered with their other leases depending on the situation.  

But I’m always looking for more ideas, what’s been working for you?

Not sure it will replace GC estimation but at least will give you an idea.