Arcanes are up to you, I prefer to always Arcane [Guardian], and then either Grace or Energize.

Some good Helminth abilities would include Roar, Eclipse, Gloom, and Pillage. Y'know, the usual.

I used to think the clone was bad, but that's because I always gave them melees. Nowadays I usually give mine a [Kuva Bramma], but plenty of options can work, such as a [Kuva Nukor] for priming or an [Opticor] for sniping in open world.