Seattle is not going to be an optimal place for cash flow (unless you buy something distressed that requires a lot of rehab work).

Every time I see a lump sum in the account it is tempting . . . tempting to borrow from it or "optimize it", or something similar. 

I have experience in supply-chain optimization and some experience in developing, but really want to work in a more acquisition-facing role like evaluating properties. 

Ask yourself who's going to buy or rent all these properties.Finally, I know the search tool here isn't optimal but there are plenty of posts that have been written about Tulum recently.

Suggest how to enhance their profile, learn dynamic pricing tools and offer to optimize them for hosts.

Apply this concept to many areas of your rental areas/homes.Good Luck and keep that momentum and optimism going!

You have to buy it with the intention of making it a LTR or second home, but then optimize by making it a STR.

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Any recommendations on what is optimal?

I would personally put a bed in the second bedroom to optimize rental income.