DOM seems to be constantly increasing.

Which means if you sell, the increase in value is completely tax free (up to $250K, the change in price).

Roughly speaking, my mortgage payment would deflate (reducing my "rent payment") or if I rented it out the rent increases would inflate, keeping the previous numbers "real."4)  Social Security @ age 62, $1,760.The above scenario does not include my taxable account of  ~ 110K, which is about 15% stocks, 10% bonds, rest high yield savings cash.  

Current tenant had a three year lease with no rent increase, which expires October this year.

Keep in mind that the minimum wage in Ontario will increase to $15/hour January 1, 2019 which should also put pressure on lower-end rental rates (which often have the best ROI). 

I’m exploring this site and real estate in particular as a way to increase our cash flow, ease up our responsibilities and increase our choices in how we live our lives.I’m particularly interested in multi family investment properties, first to move my 22 out of my house (anyone familiar with Denver will know the housing cost situation here is tough), and second for passive income streams and equity building for my children’s future. 

I'd take a portion of it and invest in stock and allow that money to increase over time.

I am afraid the increase in interest rates are no helping.

Those residents pay a flat fee based on a few factors (i.e. number of fixtures, square footage, etc.).I assume you did your research on what you could rent this for...As is, I would not pursue this deal unless you are banking on appreciation and being able to increase the rent quickly. 

I've considered two options: pay off the loan on my investment property, therefore increasing my monthly income; or put the money toward a down payment on one or two other properties.