Any suggestions on how to prevent this in the future?

His timeline doesn't make sense to me, so you might get lucky and find a 25 year old power of attorney that may or may not be enforceable in your situation, but you also might find one that is much more recent and put in place to prevent the transaction you are trying to engage in.

Does this include some preventative measure to avoid those late-night maintenance requests?

I feel like I could have done better in the due diligence stage, so what have you done to prevent these types of situations?

My concern with the more expensive property is that it would eat up most of my savings, preventing me from purchasing another property unless I find an alternative financing source.

It's not preventing me from buying, but I have adjusted the way I deal with tenants. 

It may not be a foolproof answer, but it will show that steps and measures were taken to prevent such calamities before they occurred.

Is it true of i accept a partial payment in the 1st and require the rest be paid by the 5th (when nys considers rent late) will this prevent me from evicting that month?

I think buying the LLC would prevent any kind of 1031 later too.

That prevents resmearing the same haze around.