just guessing on this one because its difficult to know exactly what you are looking for.
#1 sounds like you need to set some keyframes on BirthRate, Life and Speed in the Inspector of the Emitter to get the particles to hang there after they hit the destination. If you are really trying to freeze them in space then add a Drag behavior to the cells. That should come close.
As for #2, I’m not sure if this does what you are asking but try the Attach to emitter slider in the Emitter controls in the Inspector. you could also try the paint tool. Paint tool is somewhat of a more controlled particle system.