Question:

...what [is] the best way to collect items for pvp

Answer:

By PVPing.

Step 1. Do battlegrounds... alot.
Step 2. Starting on the 27th, buy S1 arena armor and the new Vindicators set for honor points.
Step 3. ???
Step 4. Profit!

Actually, step 3 would be start arena teams, invite people who just hit 70 like yourself, loose alot, get a few points, start getting season 3 items, etc.

Edit: Guy above beat me to it... also, Step 5: Keep fling posted on how you do in arenas, haven't heard much on warlock teams there one way or another. Good luck!