Single family residence in Los Angeles (built in 1962) has only 1 covered parking spot, and a second cannot be added.Do I have to comply with current parking requirements (2 spots) to add a detached accessory structure for storage etc. 

No. its a SFH with an accessory dwelling unit. 

Torrance currently has zoning code that covers accessory dwelling units (ADUs) that I would like to take advantage of to permit the rec room as a dwelling so that I can live in it and rent out the main house.

As some others have said paint the bathroom with a color that is going to provide some contrast (interest) and then add some accessories for pops of color, add shower curtain, etc.

Other options are rowhouses with accessory apartments in DC or single families with accessory apartments in Montgomery County.

And if possible also build an accessory apartment on our new home and rent that out.What say ye BP?

At a residential facility I work at clients often try to vape in their rooms.

I have a new tenant that wants to vape.  

Much of the regulation applies to renting out individual rooms and/or short term rentals in an accessory dwelling unit(attached or detached ADU on the property. https://www.oregonlive.com/portland/index.ssf/2018/08/80_percent_of_portland_airbnb-.htmlAs a side note,  CM2 land on SE Belmont is a prime zoning for building plexes. 

Check to see what counts as an accessory dwelling in Brantford - this would be a triplex in all but name and might be easier permit wise.