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My rule of thumb is no more than $1M property value in an LLC.

I feel like Ive heard that the rules have changed recently with tax delinquent properties in terms of how long you have to wait to take full ownership?

We recently published a video on how to avoid the Hobby Loss Rule.

But the fact is I'm building in tennessee and their govt rules are just as bad if not worse. 

My building has the 2 out of every 5 year rental rule.

This is because collecting rent is often seen as passive income, and the state may not consider this "doing business" that would trigger the registration requirement.However, states like California or New York may have specific rules, so it's wise to check state-specific requirements.Active Income (e.g., House Flipping):Active Business Operations: If you are engaging in activities like house flipping, property development, or property management, this would likely be considered active business operations.

As far as sprinklers in rehabs, is there a hard and fast rule used?

I do see the 1% rule in 80,000-150,000 range in Memphis

A 1031 exchange requires a fiduciary to receive the money and has strict rules around the whole process.