Similar I had jurisdiction architect approve a sheer wall to ceiling but inspector required it to go to shingles.

The insurance check is based on replacing asphalt shingles.

Then, think of only buying houses etc. in the fire zones that are made out of concrete and steel and cinder blocks, without asphalt or wooden shingles.

Are the shingles half price?

I am looking for thoughts on whether I should be proactive with replacing a 20yr+ old roof (missing shingles, multiple layers, looks terrible) and a 25yr+ old hvac.

I am risk averse and if I were to purchase, I would tear down to the studs and do a full rehab {this would include getting rid of asbestos shingles and insulation).1) I have done a ton of research and it appears as if getting rid of asbestos is very DIY able assuming you spend money on the safety equipment and use it properly. 

I would like to get a quote for insurance.6 unit single story building.  1960's construction, all brick exterior, cement slab, and new asphalt shingle roof. 

Lastly, is it possible to put a “seal” on a current shingled roof, should there be any leaks?

Google street view doesn't show you that....or ends up that street view picture was from 2013, and when you drive in 2024 you find someone has dumped 1000 houses worth of used shingles there.Be careful and be smart. 

An asphalt shingle roof often lasts 25 yrs, so you need to reserve $27/mo EVERY MONTH for 25 years to have $8k available in 25 yrs.