The two passives are must have, alway active and very, very useful, especially for a tank. More resources AND more regen (via light/medium passives with one light and one medium) ? Bonus resources for each synergy, when a tank use a lot of synergy ? Definitively, yes.

For the active skills, inner fire with the magicka morph is awesome. For a lot of enemies, you will not be able to taunt them at short range, so inner fire is a must have.
Bone shield is… good, but not as good as some other abilities. The synergy is very good and useful in a few situation (when the boss burst your team), but a good healer can do better and there is often something better to do. Moreover, allies rarely use the synergy because it's a dps loss, especially with random players.

The taunt, definitely. The shield, meh...6 second duration makes it honestly better for your group than you (10 second synergy)

Necrotic has situational uses.

Place points into the on that gives healing for synergy - you should have lots of opportunity to press 'X'

The one for bonus health with mixed armor should have one point right away (1% is 1%), but don't worry about necessarily actually having mixed armor until later, if you wish.

You'll end up finding more than enough skillpoints/skyshards to fill out this line as you wish along the way.