I find the most challenging part is to understand the health of the HOA. 

Challenges?

How do I handle the rehab with renters in the house or is it advisable to let their lease end and have them vacate before I take on the rehab (since the additional bedroom and bath would be for a new tenant anyway? 

You let the title company handle all the paperwork.

Why is it that people can't seem to handle anything?

I've read through the BP forums there are some challenges on getting financing for agricultural zoned property.

So it's not constrained to being an all-cash operation.The only issue I can think of immediately is that it may be challenging converting Canadian dollars to USD.

As far as landlord-friendly, I'm a landlord and I haven't come across anything unusual about Colorado that would make it particularly challenging to be a landlord.

Ultimately, I went with site-built, as there were challenges to the site. 

That's a great way to connect with others who have similar goals, challenges, etc.