A few questions on skills

I searched all over and couldn't find this anywhere... sorry if its been covered.
When I try to get a new skill in town it says it will cost a skill point. When I get a skill from a mission, I get it automaticly. Does this mean it is better to get all my skills from missions?

How does the unlocking skills thing work? I noticed its really important for the pvp only chars to have them unlocked. If I delete a char will his skills still be available? 4 isnt a lot of chars.

Thank you for your help

First question: Duh. That is why you should quest your butt off looking for free skills. Some skills are trainer only, though. I am not sure which ones, so I pee my pants every time I buy a new skill, praying that it won't be a future quest reward. I have a theory, though. When I visit the Skill Trainer, one skill is always highlighted. I am guessing that self-highlighted (it is selected when you open skill purchase menu) are skill trainer only.

Two, whenever you buy, get from a quest reward, or otherwise gain access to a skill, your account "unlocks it." From then on, whether or not you have the character, your PvP custom character will be able to use skills previously unlocked, even if you have no current characters with those skills. That's what I hear anyways.