It is difficult because you have to replace them at new value. 

I completed a 1031 exchange two years ago, but found the strict time limits made it difficult to find a good deal.

Each unit in teh building has their own master water shutoff valve, so I can't imagine it will be that difficult to get some hardware + automated billing system through someone.

It's easy to say you'll raise rents to market rate but pulling that off can be difficult in softer markets with supply/demand dynamics without causing temporary vacancies, which leads to new TI's and other lease incentives to refill the space.I'm sure you have an investment strategy for the replacement property, and that should include which markets you are looking to reinvest in.

How long/difficult was this process.

A few points, different tax laws and language barriers made it more difficult.  

Think of it this way: if we were to screen tenants on criminal background, credit, eviction history, landlord references, and income (3X that of rent and employee verified), even with 25 tenant applications, it's difficult to find a reliable tenant to match all those criteria.

Don't take care of them and you will find it difficult to keep occupied. 

I’m a newbie, I’ve always dreamt of buying multi-family units & now I’m finally at a place where I have proof of income and make decent money. upon further research, here in Florida it’s difficult to find any without major rehab work.

As a newbie back then, I couldn’t understand why it was so difficult as a hands off investor and why every single PM either bailed on me or stole from me.