If they don't leave a message, I callback and say I missed the call but if it's an employer/switchboard number it's a loss.

They are not crazy common but you'll see them every now and again.

I will definitely be employing these methods that you have recommended.

Understanding that not all pre-approvals are the same, what are some requirements or questions I can ask to ensure that the lender has actually run a credit check, verified employment, etc?

I don't know how common of a pratice this is but you could always create a single-LLC for yourself then using that single-LLC, "invest" in the multi-LLC with your friend.

Some people ask about foreclosures in Canada, here is an email I got from an expert in Ontario refering specifically to multiplex properties:"Foreclosures are rare in Canada and Power of Sale is more common.

Common practice here is that people use the standard RE contract and modify the terms by an addendum.

I think this is pretty conservative in case I run into the high turnover and major repairs which are sometimes more common in these types of rentals.I also believe buying properties at such low purchase prices allow newbies (like me) to learn and make mistakes without taking huge risks.

How common is it to sign a 6 month contract with a real estate agent?

There are always anomalies, and I will never say never, but this type of deal needs to be fully scrutinized as cost over runs are very common and generally extreme.