Returning to game... some basic questions

I played a bit in the original game and have come back to try more. I have a few basic questions that I hope people can answer quickly.

(1) If I unlock skills with faction in random arenas, does that skill become available to me in PvE?

(1a) If not, is there a way to get elite skills in PvP to translate to a PvE character?

(2) I saw that there is a hero in the nightfall expansion. Is he kind of like a pet? Are any of them available for other campaigns?

(3) Do similar insignias stack?

Thanks guys, it's been a long time since I have played and I've been having fun, while being confused in the process.

1. nope, any skills unlocked in PvP stay in PvP
1a. Cap them form bosses them
2. Just an advanced henchie, you can control their skill bar.
3. I think so, im not so sure.

There are Heroes in Nightfall and the Eye of the North expansion - not just one. You can think of them as being customizable henchmen. Each human in a party can take up to 3 heroes. You can equip the hero's skill bar with whatever you chose, and give then whatever weapons you want. They're armor can also be equipped with Insignias and Runes. My best advice with heroes is to choose which ones you want to use and fully equip them - too many people just use them with their default equipment and/or give them crap weapons they have kicking around, and then complain that they suck.

Not sure what you mean here, but, if you put, for example, a Survivor Insignia on each piece of your armor, they will add up to a +40 health bonus (+5 +15 +5 +10 +5). Some, have a global effect though, and are "non-stacking" Go here - http://gw.gamewikis.org/wiki/Insignia - for more info.

I'm not familiar enough with PvP to answer your other questions. But, it's possible that, once you "unlock" a skill, it's available from any skill trainer without having to get to the point in the game where it would normally be available.

1)Skills unlocked with balth faction become instantly available to all your pvp characters. Your pve characters will still have to buy them off a skill trainer, or buy using a tome.
1a)Elite tomes.
2)Heroes are advanced henchmen whose skillbar and attributes you set, along with their weapons and the runes/insignias on their armor. You can even micro-manage their aggressiveness, their movement and the use of their skillbars. Also there are multiple heroes available in NF and GW:EN. If you have NF, there's also a hero in Cantha and Tyria you can obtain.