Cor, most papers except "waterleaf" are sized in the making, and the tests
I did with at least 20 different kinds of artists' paper showed *no
improvement* with an added starch-type size for cyanotype, and an actual
disimprovement for an added gelatine size.
Yes, smoother paper = sharper image. Which side to use depends on the
paper & your preferences & which side you accidentally land on. Some
papers have a noticeable difference in texture (the "wrong" side is
usually smoother, but may show mechanical texture of the wire). And not
only do different papers all by themselves give different colors (from a
greenish blue, to a rich almost midnight blue) they also have different
scale. Some are quite contrasty, so you could print a thinner negative on
them.
Another nice paper is a good writing paper -- almost any typing paper with
a rag content.
Enjoy,
Judy