If my friend and I chose the same storyline when we create the characters, can we do our personal stories together? Will the progression for each of us be saved?
You can, but you have to be sure to have the same level range. Story chapters unlock every 10 levels. If you are level 39 and your friend is level 40 and runs a story mission which unlocks at level 40, progress will not be saved for you. And you have to be at the same story-setp. If you run story-missions together and your friend decides to do one step-alone, he is one step ahead of you = progress will not be saved for you.
I do not know if it can be done during the first act (level 10 and level 30), if you play two different races. But if you play the same race, it should work as well.
It is not difficult to set up. Enjoy.
Anyone can join another player in their personal story, even if it's a storyline their character doesn't have access to (for example an asura can help a charr with their level 10 story). If the other person - the one who doesn't click to enter the instance - is on the same story step they will be given the option to accept credit for it at the end, and then their story will progress too.
There are two biography questions which determine your level 10 and level 20 story, so you'll need to have picked the same answers there to get the same story. For humans this is your social class (noble, commoner or street rat) and your one regret (dead parents, dead sister or not joining the circus). At level 30 your story is determined by your race (so all humans get the same one), at level 40-60 it's the Order you join (Whispers, Priory or Vigil) at level 70 its your greatest fear (chosen during the level 60 story) and at level 80 it's the same for everyone. There are also other choices you make during the story which will affect it for 1-3 instances. For example during the level 30 story you have to choose which of two Orders to work with, and each choice gives you a different instance to play.
If you want to make all the same choices then it's just a matter of the other person picking to accept credit at the end. If you want to make different choices at any point you will need to do the instance again, and then do any differing story steps separately (or play both versions together) before you join up again.
All of the choices are permanent but the only one that has consequences beyond the story and minor things like which NPCs appear in your home instance is the Order you join. Even then it's fairly minor, you get access to that orders weapon and armour skins and an extra area in their base and you sometimes get extra dialogue with NPCs both in the story and in the open-world. (If you run another character through the story you can pick a different order so you could eventually get access to all 3 on your account, you just need to remember which character/s are in which Order.)
"Hard knocks, bad luck, been knocked down,
You got back up, rise up, shine on, keep on fighting, the war is almost done...But then I hear you're gone.
I feel, when the lights go down, you are still here, all you hold dear remains.
Your star never fades."
Awesome. Thanks all.