Ok so I saw a guy in pvp using a stabby and shooty weapon, and he was by far the most dangerous enemy at the time not because of his power those were annoying to though. When he attacked he could use both gun epic talents and and melee epic talents. It was insane he just kept hitting me with burst fire, double tap, relentless, and others pains. I have a slashy and staffy weapon and my question is that can I use staffy epic talents with my slashy and staffy weapon like mojo echo and other staffy epic talents?
The short answer is yes, you can combine staffy talents with slashy talents. However, readied spell and coward's bane will not work if you have a melee weapon of any sort. Mojo echo and mojo rising on a pet are probably the most useful staffy talents overall.
One place to find complimentary powers and talents are the "hidden" trainers in Corsair's Channel. To get these specific talents and powers you will need Practice Points or you may have to redo your powers and talents.