1. No. (unless you can afford to brick it should the worst happen - which it can. wait until the insider program expands to include the 1520, there is a reason it only includes a specific subset of phones first. and its not because MS is stupid or wants to screw all but certain models.)
2. No. (actually, its meh, or so I've heard. you could probably tolerate it, but plenty of small things are broken.)
3. Don't think you can anymore.