You are only able to trade share's during specific windows of time typically 1 week after earnings are released.
Additionally virtually every company I've known has explicit policies stating that you cannot buy/sell any derivatives related to the company stock (which is a shame since buying put options is a legitimate way to insure your compensation).
Further more, even these rules are only this lax for non-executive or other high level employees. If you're higher up in the company you have much more access to non-public material information. The solution to this is usually to set up a 10b5-1 that automatically liquidates shares based on a schedule approved by the board.
In regards to the "previously" question. I wouldn't worry about legitimate trades, but if you are trading based on insider information and looking to gain a lot of money, then trading would, by definition, be "insider trading"
As a practical matter, you can set up a 10b5-1 to get around this restriction if all you want to do is regularly sell your RSUs when you get them or at certain fixed periods.
Just having RSUs doesn't mean that you are trade restricted. That depends on your job function and you can confirm with HR (I had to). In addition, like you say, there are further restrictions if you are sufficiently high up.
Yeah, some companies have restrictions on derivatives, most have restrictions on shorting.