@Jay Scott It's good that you've got the gears turning in your head. Without putting too much thought into this, my 'thousand foot aerial view' is this....
It sounds like you are in an expensive / higher end location outside of Seattle. What is keeping you there? Jobs? Family? Schools?
For that size house for just four people (Wife, two younger kids and you), it sounds like a lot and could be a good opportunity to downsize. Are there more reasonably priced areas in your region that you and the family could downsize too?
I believe HELOCs are great when...
A) Rates are decent
B) You have plenty of equity to get you a decent pile of cash to play with
C) You would like to stay in your house / keep the property long term.
For your situation, I would lean toward selling your house on-market, cashing out, moving to another region where the housing is more affordable than +$1million dollar appraised homes, pay cash for your new home, then with the leftover cash, buy one rental and see how it works out for you.
Paying cash allows you to negotiate better on the property and is more enticing to sellers. But you need to make sure you and your agent are confident you're not overpaying.
Now, all that being said, I also think it would be a great idea to do some value add projects to the properties (Personal residence and rental property) and do cash-out-refinances on the buildings when rates become more favorable and you're up and running with the rental. Rinse, repeat for another property.
All that said, this is just my OPINION without diving too deep into your situation. Best of luck!
- Troy