The structure of prion can be described as an abnormally folded protein. They do not reproduce, but can propogate by changing other proteins to have the same altered protein structure. Sorry don't know about size for them.
The structure of protozoa can be described as single-celled eukaryotic organisms with internal membranes. They generally reproduce asexually via binary fission where the organelles are replicated and then the protozoan divides. Some types of protozoa also reproduce sexually via the creation of gametes and fertilisation etc. Most protozoa are less than 50 μm in size.