The kitchen boasts a double oven, glass cooktop, and a dishwasher.

Your renovation number seems very low for a newbie trying to get this done in Ontario: you'll have to split the single-family and then also put in another kitchen and bathroom, manage the heating somehow and then gas and water.

I see that all too often in bathrooms and kitchens.

Never built anything that small, as the incremental cost to go from say 800-1200sf is not a significant cost since the major factors in a home are the MEP's, kitchens and baths.

For the apartment space, there are currently no actual bedrooms so I didn't think about renting by the bedroom, it has 1 full bath and kitchen on 2nd floor and then a living room and deck on 3rd floor.

-does the interior need cosmetic updates - paint, carpet, lighting, or even heavier cosmetics - appliances, kitchens, bathrooms?

The nice part is, I renovated the whole thing in 2020(new shingle roof, new siding, new heating system, new HW tank, new kitchen, etc.) so I dont foresee any big CapEx expenses in the near future.

Before it was rented I added kitchen cabinets and a counter where there was none, remodeled the bathroom (not a complete makeover, but substantial), added a dishwasher and installed flooring.  

My mortgage is very low and I have just remodeled the kitchen and remaining upgrades will cost less than $5k.

Hi I am currently saving to fixing up my rental property the first place I wanted to start is the kitchen.