Guild Wars 2

When u go in DS,use #2 #3 then #5 and #4.

Now for the questions:
1)Yep,#2 is awesome spell,also as u have full rabid even close to target u are able to take some hits.Just use ur dodge and take some distance again.
2)#4 in condition builds can be used offensively and defensively.Offensively cause when u are in DS,ur crit chance is higher (minor trait #2 in curses) + rabid provides some really good crit chance.Now combining sigil of earth and minor trait #1 in curses you can apply bleed on crits so u end up with 3-4 bleeds.Also u can use this skill defensively as u get life force and in that build life force regen is kinda a problem.So if u dont have enough life force u can use this.
3)No,dont stay in DS for life blast.As i said,life force regen is kinda a problem in that build so save as much life force u can.If your health is really low then stay in DS and spam this till enemy is down or ur heal is up.

For lvling power is better.
For dungeons power is better.
For spvp/roam/solo/small fights in WvW conditions are better.
For WvW (Zerg vs Zerg) power is better.

Depends on what u want to do in WvW and the fights.If you want to solo,roam or play small fights better go for a condition/terror build.If you play mostly Zerg vs Zerg then power necromancer is better,more reliable dmg.