From my experience so far, maelstorm works best when you bring attention away from the poison aspect and focus in on the physical damage of it

A few points to note about maelstorm:
1). Every 1 of those little poison spirits has a chance to hit a monster. (this means if you cast maelstorm and it shoots our 3 spiraling waves of spirits, each little bastard has a chance)
2). Each little poison spirit, if it hits, applies that 3/4 physical weapon damage including any modifiers.
3). The skill is IAS based
4). The skill is AR based (meaning every little spirit has a chance to hit a monster based on your AR)
5). DS, OW, CB, and % enhanced damage, and +min-max damage affixes from items apply to the physical aspect of your maelstorm skill

With that being said, I think focusing on mods that you would focus on as a melee char would be best for this build. In addition to this, you will achieve your survivability through various methods such as golem, merc, confuse curse to begin a battle, revives, etc.

I will finish by saying that maelstorm is a supplementary skill (depending who you're fighting). Corpse Explosion will always be the best damage dealer when it comes to big mobs.

Don't have much time otherwise I would list you skills/stats/etc, but thought I would share a few thoughts regarding maelstorm. Hope it helps!