Suggestion 3 is particularly terrible, since the concrete skeleton of a parking garage is really poorly suited for conversion to housing. Utilities will require raised floors and drop ceilings even for arterial needs. The size of the building footprint is unreasonable for general residential division - leaving either large interior space vacuums (which can cause safety issues especially when lacking natural light) or units with no external wall (causing a different set of health issues and probably massive fire code violations). The material to be built on will be contaminated oil soaked concrete (the sort of material they truck out of former gas stations before any other kind of construction can commence). And, lastly, parking garages aren't structured to allow a structural wall free perimeter which means that temperature control within such a building would have to be entirely artificially done - so A/C and heat 24/7.

It is much more cost effective and environmentally friendly to tear down parking garages and replace them with new construction.

For 1 - sure yea, I sorta doubt developers are going to voluntarily go below 1 space/unit in any sort of world because the value of the property takes a steep dive - but removing any commercial unit parking requirements or higher requirements for larger residential units makes sense. I think 2 is great - assuming exceptions are made to support park & ride demand. 4... Eh, EV is going to need to solve this through market forces so I think we can entirely ignore this (though I would love to see a lot more EVs I think this is point is entirely tangential to the main discussion) Lastly for 5 - nope. Every building ever has managed to sort this out naturally without regulation... leave this up to the market.