The bottom of the sheetrock was penetrated in a lot of areas so we elected to remove the bottom four feet of sheetrock throughout the house.The fiberglass insulation mostly survived, but why chance it? 

Fiberglass tubs would not cause a weight issue compared with the old cast iron tubs, and one questions is will it fit in the door, up the stairs, and into the space, the tubs now can come with surrounds that have sections to help around those issues.As a renter a shower is preferred for use.

All the main pipe runs in the basement tend to be covered with asbestos.Alot of times it has been removed and hopefully replaced with fiberglass but again it left undisturbed it doesn't pose a threat.

Probably 2 long, parallel onesBathroom 7000Replace flooring with LVP (waterproof kind), if vanity can be saved - save, sand and paint, replace counter top with manufactured quartz, replace sink, replace plumbing, replace faucet, replace lighting, replace bathtub with new fiberglass bathtub and tiles around the shower area (builder grade)Flooring @ 2 a sqftSave if possible, clean, if damaged, replace.

You need to insulate within that cavity with unfaced fiberglass insulation, and then when you put in the window, you will generally want to use Great Stuff window and door expanding foam along the sides as well.

I really like their Integrity line of fiberglass windows with wood interior.

If you can afford the fiberglass frames, they are higher quality than vinyl.

The plumber found out that the fiberglass bath tub upstairs has 4 cracks and had been cover by glue and was done professionally.

In 1977 they started using copper water lines, fiberglass insulation (no more asbestos) and lead free paint,,, a superior product all around.

Install the fiberglass tub, new drain/overflow, single handle mixer valve, and fiberglass surround.