But make sure you make a file labeled "why I intended to hold this and what changed".

It depends what basis you are filing under.

Security systems are easily outsmarted, that’s the point of the initial visit, to case the joint. 

This allows for proper retirement of assets.If a property has already been sold it may still be a good candidate for cost segregation as long as you sold the building and have not filed the tax return.

Consider using an FHA loan to secure a 1–4 unit property with just 3.5% down and take advantage of tax benefits by living there for at least two years.

I'm going to reiterate what's already been mentioned above, but I'm going to actually give you examples of why it's relevant to you to find a U.S. tax professional.1 - You're going to need to file U.S. taxes once you have property down here, there's federal filings, state filings, and sometimes local filings too2 - Tons of tax treaties between the U.S. and Canada that are easy to miss and can cost you a lot of money (important one with rentals - effectively connected income - if the professional you talk to doesn't know what this is, run away)3 - The amount of days you spend in the U.S. needs to be tracked and if you go over a threshold, all of your worldwide income could be taxable by the U.S.4 - Selling real property means up to 15% of your sales proceeds might not be available to you for years (FIRPTA)5 - Lots of nuance at the state and local levels, which both want to take as much money from you as possibleMain takeaway here is that you should find a U.S. based tax person.

As soon as a tenant fails to pay rent, you can file a complaint without waiting 30 days or issuing a separate notice (unless your lease requires one).That being said, it could be a waste of time/fees to run to court because tenants in NJ may come even on rent (even after you win the eviction case) and then they won't be evicted: “The tenant shall have three business days after service of the warrant for removal to pay all rent due.”

The area has certain advantages like shelter from regulation risk (pretty much as low as anywhere in the country if you buy in the approved STR tourist zones) and long term security (people aren't going to stop going to Orlando anytime soon). 

I know that the general guidance is that emergency funds aren't to be invested, but given our financial security and the fact that we already have a personal e-fund in a safe, non-volatile location, would it still be crazy/unwise to invest this 15k in an S&P500 index fund in a brokerage? 

I am expecting a day of reckoning for this model in the coming years when an LP decides to file a lawsuit based on misrepresentation which traces back to the teaching techniques of the coach/mentors who are essentially offering pay for Co-GP title courses where the students are taught they can use their GP title to raise money.