I wanted to know if my student loans will have a big impact on my ability to get the cash out refinances for my rental properties.

This can impact your ability to sell later and the potential for appreciation.2.  

Yes, if it is a mass tragedy you're going to be waiting on a payout as insurers become impacted... but you're going to get your market value or replacement cost. 

The problem with that at scale is it impacts their businesses.

I have no idea the impact the new laws have on me, as my taxable income was significantly higher in 2018 than in 2017. 

The impact of UDFI in an IRA is typically nominal, so while a 401(k) is better through avoiding that tax, it is not generally a huge differential that would encourage one only eligible for an IRA to run away from a leveraged transaction.When you read on the internet that a Solo 401(k) is exempt from UBIT, that is a broad statement that mis-characterizes the real difference.  

ROI will be through the roof.All three can be implemented today and will have an impact on your business.

That obviously can make a huge impact on the ability of a unit to be rented.  

How big a problem would it be if they did so, in terms of financial impact / wasted time / etc.?

Low impact tenants are lawyers, CPA, financial professionals, etc.