I live in a rental apartment and would like to use the dots on my appliances are they easy to remove?

Yes they are very easy to remove. I use them on my air fryer since it is only a touch screen and if unable to read the buttons these were great. They come in different shapes and styles so that you can use different ones for temperature versus time, and the individual settings like the start and various categories, I also use them on my washer and dryer and I’m sure you can use them on microwaves and pretty much any appliance, they are definitely a lifesaver!

Are the stickers waterproof? I need them for measuring cups and other kitchen items

They should work for that - the pieces are just gooey plastic, but the adhesive may eventually wear off if they get TOO wet. We use the around the kitchen with no problem but doubt they’d make it thru the dishwasher…they’re inexpensive though, so worth trying. Another idea: have someone put dots of glue (with a hot glue gun) on spots you need…you can peel dried hot glue off plastic, but it should stay as long as you don’t intentionally pull it off. Good luck, hope that helps!

Tiny ones for my laptop to be able to close without activating the screen reader. How small do these bump dots get?

They are small. I got them for mom’s remote control buttons. She can’t see well. The down side is that they can’t be handled like I wanted because the glue is not super sticky. I ended up getting a batch of mixed sizes and they worked better because of better glue.

A blind friend needs to differentiate between a large set of different house keys. Are these small enough to fit on the flat part of the key’s top?

I am not quite blind, but use there dots mark what buuttons to use on appliances. A dot might work for one, but I don't know if the size difference is enough to choose different keys. Why not try velcro on another key?