I guess its not early game anymore, but I just starting Act 2. Its seems like my gear have a lot of rune slots. I am trying the discard the mmo feeling of not slotting till the end game, but is it vital to slot those gear for the extra push? I have no trouble with the first group of enemies (the big voidwoken mobs) but just in case its gonna too hard.

You can extract runes at any time without penalty or material cost, so if you've got runes there's no reason not to make use of them. It's not necessary, but there's no downside either.

Just remember to remove them before selling your old stuff!