Hello! I started playing GW again and I can't remember mostly anything about it
So here's the questions :
Should I run first the campaing trough before making PvP char?
Nah. You can make a PvP character at any time. I made my first one when I had reached Lion's Arch.
Just remember that the only way to get good at PvP is to play it. Being good at PvE is not the same as PvP. Pratice Pratice Pratice.
Rangers can really be good in PvE without using their secondary. I'd suggest all ranger skills and a monk reserection spell like rebirth.
also for a good pvp you need have unlocked pvp skills ( by balth factions or pve).so before think about a pvp ranger build make sure you have the skills for.
about the ranger build it's all dependant of what you like.
you can go with this :