Here is one last version of this spell.
Arms of the Goddess
Arms of the Goddess SPELL 1
Traditions divine, primal, occult
Cast [two-actions] somatic, verbal; Duration 1 hour
Translucent arms of force appear behind you. These arms can carry weapons or shields and can be used to cast spells. You can reduce the number of actions one spell can be cast by by one somatic action each turn. You can reduce your multi attack penalty by 1 for one attack each round.
Heightened (4th) you reduce your multi attack penalty by one for each attack you make in a round.
Heightened (6th) all somatic actions can be performed by the hands to a minimum of one action for a spell.
Thoughts?
Throat Punch Games 
I like it! The only change I would make is at the base level remove the removal of the attack penalty, but leave it for the heightened. I think of it like the Kasatha in Starfinder, they have 4 arms and are able to put a weapon in each one, and allows them to use ranged and melee weapons without having to drop or sheath them. That is a huge benefit.