Good questions, I guess!
Are you an Auror?
Technically no, I just pretend I am as part of my parents' convoluted tax avoidance scheme.
Do any Solar Shadow (SS) characters have canon counterparts? From 1 to 4?
A lot of canon characters later appeared in SS -- Selena Daria, Serenity, Aidan, Eron, Shinica, Valerie and Ataraxis all appear in various places in the SS universe. Ilina, Elektra, the three Goddesses and a few others were supposed to appear in SS3, but I never finished it so they didn't. Finally, Shinova, an obscure character who is canon but never appears in Lunar Shadow is briefly mentioned in SS4.
The only character to appear first in SS and later be confirmed canon in LS is Andrea, who appears as a friendly NPC in Selenic Shadow.
There are two characters who definitely do not have canon counterparts and who never will: Terrah, who doesn't exist in LS because he doesn't fit into the canon Horton family tree, and Mitsuru, a character who was accidentally created by Alfasketer due to confusion over some dialogue in the original Lunar Shadow. Technically, her canon counterpart is Hiranya, but in SS she and Hiranya both exist as separate characters.
Also, when was Andrea born?
I like to think of her as slightly older than Selena Daria -- so, most likely sometime in the early 1980s. So, she is in her early 30s at the time of Lunar Shadow, and roughly 40 by the time she appears in SS2.
And, seeing as these Valkyrie taint things have different variations, what would hers be?
The Valkyrie taint things only really apply to the Horton line, I believe. She doesn't appear to be related to them, so she doesn't really have one -- she only has the standard abilities of a Valkyrie.