1. Yes, of course. No government, religion, or society should have control over another's life or death. See below.
2. Yes. And yes mental illness like depression should qualify (See below). But mental illnesses where person is extremely disillusioned should not.
3. Yes. Appearance sure, it is their life.
4. Sure, see below.
However, I think person who is committing suicide still has responsibilities to society including not causing emotional harm to their loved ones, not leaving a mess behind for others to clean up etc. As a society, we should establish guidelines for suicide. I like Hindu practice of suicide called [Prayopavesa][1].
Prayopavesa is basically slow suicide by fasting to death. This may take days or weeks. This solves the big problem of people changing their mind after pulling the trigger or jumping off the ledge. If at any point suicidal person changes their mind, they can start eating.
Also if a person is disciplined enough to fast for days, we can trust that person has emotional maturity to make such a big decision. In other forms of assisted suicide like injecting drugs, an emotional person may sign up with a service, then they might even go through extensive paperwork. I personally end up doing things like sky diving just because I signed up to do them while drunk. I didn't want to do it later, but felt ashamed asking for refund. I imagine, emotionally unstable person may go through paperwork even when they are having second thoughts.
[1]: https://en.wikipedia.org/wiki/Prayopavesa