However, since I haven't gotten an LTR in there, my choices now are to relist it for sale (the market is slowing), or invest $15k or more into furnishing it.

The best choice depends on how much control you want to keep and what type of return your investors are looking for.

This is the Sacramento appreciation for this century (pretty good, but not special for CA) https://www.neighborhoodscout.com/ca/sacramento/real-estate2) property tax has gone up at most 2% a year.3) rents have increased $951.00 this century which is the average rent increase for this century for Sacramento.My market meets all  3 of these conditions, but it would not be a good choice for the OP.Sacramento is a fine RE market.  

It feels like owning a mix of apartments and dividend-paying stocks, but tied to something essential: energy.Curious—has anyone here added royalties (or other “alternative” passive income streams) to your portfolio alongside real estate?

I think in most markets, 3 nicely appointed modest properties will perform over the long run better than a big fancy one.If I had my choice, I would have 3 lake houses like I have now rather than a single lake mansion.

that's the question to be addressed - opportunity zones as an alternative for 1031s?

Yes, you're missing the underlying appreciation of the house, the value of storing money in a physical asset versus an alternative and capex costs.

Relocators can be good choices for you too. 

Ryan Coon may know better but the way he has expressed his advice could cause an investor to make some bad choices.

"BiggerPockets" is a popular choice, offering a wealth of information from industry experts.Networking: Joining local real estate investment groups or online forums can be incredibly beneficial.