I used to work for a company that does asbestos abatement. The thing about asbestos is that the particles are ultra fine. Like pass through any filter that isn’t HEPA with ease.

So, if you try to abate it yourself without complete saturation of the media, you will end up with the particles hanging around for a long time.

Mesothelioma from asbestos comes about from long term exposure. Most people do not have a problem with short term exposure.

Point is, if you’re going to remove any material that might contain asbestos, you better make damn sure it’s really wet all the way through.

Odds are the OP’s building was built after 1979-83 anyway, so it’s probably not a concern. Side note, asbestos has not been phased out in some parts of the world. So that assumption is not necessarily valid outside the U.S. or Europe.

Asbestos stopped being used in commercial and residential construction in 1979. I usually say if it’s built after 1983 (some builders continued to use the products they had stockpiled), it’s highly unlikely to contain asbestos.

Additionally, most cities and even some towns have testing labs. You bring in a sample and they’ll test it for $30-50.

A few things, the drywall is probably mounted to metal rails that are attached in a perpendicular manner to the joists. This is very common in multi family building. It helps suppress sound transmission between the floors.

Find the AC register. It will most likely be be attached to a joist. Once you find one, the others will be 16” or 24” away.

Well, foam insulation has the highest R-value by volume as far as I know. I build custom homes for a living. I always recommend foam to my customers because it works so much better than any other readily available products I can access.

Spray foam insulation would work the best in this instance in my opinion.

I’ve read 4 or 5 of Reverte’s books. I enjoyed them all. I’d recommend The Flanders Panel.