Yes, the acetal is fairly easily removed by aqueous acid. I realize when you’re learning organic chemistry, textbooks can be fairly careless about H3O+. It can be used for hydration of alkenes, hydrolysis of acetals, or simple workup of a basic solution (e.g. Grignard reaction), but you’re not really given any gauge on the relative reactivity of any of these processes.

In practice it takes a pretty concentrated acid to hydrate the alkene, whereas a dimethyl acetal is readily hydrolyzed with H3O+. I suppose for a situation like this it might make it better to say, “mild acid?”. If it were “concentrated H2SO4, H2O” then I would see hydration as a significant process.

Noted. Thanks for the suggestion.

No, because it isn’t possible to form the ylide if there are no C-H bonds on the carbon attached to the P.

Generally esters don’t react with ylides. To form a new =CH2 bond with the C=O of the ester you’d have to use something like the Tebbe reagent.

That’s a good question. I usually see the other way around – a carbene reacting with a heteroatom to give an ylide.
There might be a pathway there. It would be a good research project.