Work with a lender that does this day in and day out.

Usually have to add the lender as well 

Sounds like they lent you the $ vs a partnership with an equity split.I give my private lenders a note (that spells out the interest rate and terms) and deed of trust for physical collateral I then make payments to them and the balance of the loan is paid off with the sale proceeds or a refi.

Generally speaking, HELOCs are more suited for personal expenses or home improvements.Also, keep in mind that most lenders right now are capping at 75% LTV for a cash out refinance, not 80% LTV.

Should I be a private lender since rates are so high?

Here is a summary of the book.https://www.nateliason.com/notes/long-distance-real-estate-investing-david-greeneThe book also mentions the importance of having a rockstar Realtor, contractor, lender, and property manager.

.- I'm happy to share my contractor, lender (conventional, construction, or hard money), property manager, etc. contacts if you do choose to continue investing in WA.

I recently came across this "FHA construction to permanent Loan" option which seems almost too good to be true, so I wanted to get some input on how this works and where I might be able to find a lender.

Hi, I am struggling finding a portfolio lender in Texas that does 10% down for a second home. 

You may run into issues with lenders as a family member is leasing the property out though.