I am in the process of building an Accessory Dwelling Unit in the backyard with a one-car garage and one-bedroom apartment that I will move into and then rent the basement to pay for the new unit. 

If you're buying an apartment complex or a mobile home park, I've seen management being part of deal itself since it's another revenue stream.

He wants to use the house as an income stream, and start investing. 

My thought, is it possible to bring this in house as an income stream like parking/ Cable/ Wifi/ etc?

By reading this, I can advise you to do your homework and don't just invest because you want/need another stream of income other than your job and try to do it all yourself.

I've co-bought a single family dwelling with my dad that was financed on a 5 year balloon payment that I intended on refinancing.

Stick to your process and accept the late fees as an extra income stream to offset your drinking habit. 

Never assume you can add another dwelling to the land until doing so.

Insurance is $33/month (liability only, I'm self insuring dwelling).   

Not just airbnb, but a mix of furnished rental income streams like corporate accounts, etc.