Question about the skill points
You can unlock an infinite number of skill points. There are more than enough available to unlock all the skills. And when you are max 80, for every level of XP you gain after that, you gain a skill point.
Not to mention the hundreds of Scrolls of Knowledge you will amass.
It’s still a good idea to try and pick the best skills as you’re levelling up, because if you make a bad choice you’re stuck with it until you’ve saved up enough skill points to get a new skill.
But that’s the worst that will happen, like other people have said you’ll get more than enough for all the skills. Once you’ve unlocked them all you can then use them as a currency to buy certain items.
“Life’s a journey, not a destination.”
You continue to earn skill points after you’ve unlocked all the skill point challenges on the map. In fact, you will have hundreds more than you need and they become a type of currency that you can use to create legendary and other named exotic weapons, ascended armors or use them to upgrade crafting materials – in effect you can sell your experience (time) to other players with those skill points or use them yourself to create unique items.