Your build is solid as it is as far as stats go for a healbot. As a healbot you will still be using offensive spells at time. At your level you should try soundburst for some cc. If you do plan on doing some offensive spells dont worry about those feats yet b/c spell resistance isn't an issue until after gainthold and you probably want to take empower spell anyways. Post gainthold however spell resisance is a huge issue. Until then you should easily banish/command/greater command/destruct mobs.

My clr (healbot) kept necro focus until he was done with gainthold (when it became a pain to get past the sr) and then I swapped it out for heighten. I very rarely use heighten but it is very useful at times.

As a pure healbot you find your self turning on heighten, extend spell, empower spell, and empower heal towards the end of some quests when you realize that your party doesn't suck and doesnt need to be healed a lot (such as the end of most hound runs).