I live in Brampton ON and am relatively new to Real-Estate but willing to work hard, so looking to connect with Greater Toronto Area (GTA) specific meet-up groups and learning material to take my passion in real-estate further.

I’ve also been networking out of state to identify specific market to begin.

I have learned a lot about the process from listening to BP podcast and other sources, but I still don't know about Oregon's specific laws surrounding wholesaling. 

What specific responsibilities does the previous manager have to ensure a smooth handover?

You have told us nothing of your specific situation and why you are asking these questions.I typically deal with investors on NNN type properties where net worth as an individual is 7,8,9 figures.

I'm not sure what the path to begin looks like, but I've been researching about different approaches, specifically multi family properties and House hacking.

So, they may have been under a month-to-month agreement all along.Either way, there should be no specific reason why you need to ever have them sign a new lease/rental agreement.

Here there is a 25 GPG hardness and .2-.8PPM (not sure specifically what my rental has), which leads to buildup and rust, in addition, there has been a history of too high magnesium which caused an advisory from the city itself about potentially unsafe levels of magnesium. 

It really depends on what your budget and specific needs are.

The property prices are lower compared to other markets, and the rental demand in certain neighborhoods can be pretty strong.Of course, it's always good to dive into specifics about the areas you're considering within Mepmhis.