You can indeed do any team comp you want so don't take me wrong but since u explained your reasoning it just feels weird you'd just stack necros. They are not really that good and cannot provide the buffs you need.

For healing ele/druid are both better and i'd prefer druid for party buffs. Druid can also tank easily and replace engi.

You need to consider the buff upkeep as well and throw a chrono in. A chrono doesn't take much away from party and gives quickness to everybody + shares other buffs on top. Can also be used as a tank if needed.

With the necro trait i dont think fury is needed that much tbh so i'll skip that.

For defense purposes get a rev to give protection and also help chrono with quickness if not tanking (comm gear)

So end result would be: Druid / Chrono / Rev / 2 Warrs and 5 necro. In this scenario druid will be using sun spirit i guess.

This type of builds are not for my taste but this is what i can suggest.

Personally if i wanted to run super-safe strats i'd put 1 ele out of groups to heal and sacrifice a dps slot from normal raid setup. If you need more setup won't save you, as people will simply get downed/die anyway.