1) Are there general guidelines as to being possesed/how would you like that played?
Well the idea behind this is that Omni's possession is not complete, you do not become Omni you become a servant of Omni. IE he effects your way of thinking, instead of going against him your ultimate goal is to assure what he wants, you want.
2)What is the cure, or will there be one?
The "Cure" For Omni's possession is a simple EMP wave. The Infection is a series of nanites that basically mess with your cerebral cortex and such. So its actually a quite simple fix. However after a longer time the changes the nanites create to your body become permanent
3)How did we get infected again?
You become infected by either being stabbed by one of Omni's original droids, or by being stabbed by another infected organic.
4)When can I attack within?
This won't be possible. When you become infected you become linked to Omni's central core. He monitors and becomes part of EVERY being meaning betrayal is impossible as once you are connected to him you literally cant go against him and once you are disconnected he knows youre no longer part of him