I’ve used it to prime interiors after plaster work but mostly used for exteriors.

I would recommend talking with your friend and seeing what he is doing so you can do something complimentary.I'd typically start with the exterior and rebranding. 

Since I purchased the home- I have been renovating both the interior and exterior.

I would just evaluate the exterior in comparison to other recently sold properties to ensure it is on the same level.

Those were a drain pan issue and a nonworking exterior heat pump that was causing a circuit breaker trip. 

On my end - I've heard that some of the easiest (and potentially cheapest) tricks could be:- applying a fresh coat of paint on the exterior / interior living room spaces of the home- refurnishing doors / door knobs - updating the lighting of bathrooms or kitchen area light fixtures- bathroom refurbishment- curb appeal / clearing out excess weeds/trees/shrubbery.I've also heard of situations where the home owner would either offer to build, or provide a backyard shed for the tenant as additional storage space, charging an extra $100-$150 per month if the tenant wanted to use it. 

I've been doing a lot of research about the whole process, but something nobody talks about is the design choices you go with for the interior and exterior of the home.I'm no interior designer, nor have I ever been in any way artistically skilled, so I'm wondering how other people like me tackle this problem. 

Is it worth it to frame the inside of the exterior walls to Insulate and put dry wall on easier?

Assume $5k per unit and count the exterior as a unit.

They cost much more in US then regular electric and the magnetic pot thing may be a  turnoff for some renters.