It's really up to you. Just remember that you will get a second weapon slot at lvl 15 that comes with it's own still bar. When you switch weapons it will switch skill bars. You can have two of the weapon with different buffs on them and the same skills, or the two of the exact same weapon and different skills, or what ever yo can make work. It's a long road to the end game so I bet sooner or later you'll find a reason to add more tools to your kit.

you can respect later

I read that an easy way to level 2 weapons at once is to use your main then switch to u're alternate weapon just before turning in a quest. That way the alternate weapon will be leveld when u get the exp points for completing a quest.