Replicate and random floating around

I want to make these little viruses and the injection replicate a few times (in varying sizes) and float around the frame randomly, making a bit of a soup of viruses (yuk).

I have tried using existing emitters and replacing the source graphic, but am not getting the results I want. I don't want them to appear, but to already be in frame, just floating around.

Any tips very welcome!
Thanks in advance.
Suzanna

Hi Suzanna, just explore 'parameter behaviour' here is an old example >
a new video with all of them >

Thanks, that is a very helpful tutorial. I'll play around.