Back after over a year, please advise.
Well, you might find it easiest to remember how to play if you start a new char up and level it. But a start on answering your questions
Traits. They no longer have stats attached to them and you now get 3 full lines. Your best bet is to go to wiki and read the section on traits
https://wiki.guildwars2.com/wiki/Trait
Go to your hero panel and mouse over the different traits in each trait line to see what they do and which trait line would be best for you.
Different abilities/weapons
If you have Heart of Thorns you can get an elite specialization (trait line) that will give you the ability to use a new weapon and its skills.
ANet may give it to you.
I see a lot of recommendations about starting up a new character and play them enough to get a hang on all the systems and how they may have changed since you were last here.
Biggest thing now are the trait rework into specializations. It’s important to note here that upon level 80, you will have enough hero points (formerly skill points) to unlock every base specialization traits and every skill on your character. You can always get there quicker by doing the hero point challenges through out the maps but it will never be a case where you don’t have enough to unlock everything upon hitting 80.
RIP City of Heroes