I will now probably change to the Darkness skill tree to tank and should I then being picking all gear with a higher Endurance, as opposed to Willpower?
Yeah, the stat focus changes. Endurance, Defense, Shield boosts, Absorption, stuff like that. You're looking to raise your health, and your defensive stats. Darkness gives you the tools for taunts/aggro management (and they're really fun and easy to master). So you then shift your build from the DPS stats to the ones that make you better defensively for when you've got the enemies' attention.
I found, in terms of tanking, the Tionese wasn't as bad as I thought it would be. The offhand shield is a solid pickup. On one of my other characters, the PVP recruit gear was better than the Tionese in a lot of spots. But for an Assassin tank, the Tionese Survivor set boosts a lot of the right stats so the Recruit gear doesn't make it pale by comparison.
The lightsaber's not all that hot compared to the recruit saberstaff. But I'd take the Tionese shield over the weapon anyways.