Im not sure. Im seeing a lot of sources saying it retains health benefits like polyphenols. But also all of the sources are olive oil industry sites...theres a bizarrely large number of different industry PR sites for olive oil apparently.

you can use it gently, the best EVOO you would just want to leave as is, but the lower quality ones would be fine for say the low temp saute you might do for a puttanesca or whatever.

No. It contains things that are temperature sensitive and can result in off flavors if overheated. A bit like butter, but in different ways.