Rachel,
Are there limitations as to the size or file type allowed?
Certainly. But I don't know if they are documented.
I can see that we can plop a jpeg in the middle of text but a PDF
appears as an attachment.
Only "image type" files can be inserted inline. I'm not sure what the full list would be, but PDF (and DOC) would be excluded.
I have someone asking me if square or rectangle matters ... I suppose
not.
Nope. Not in messages or wiki pages.
She also is questioning the file size requirements.
In the Photos section of your group's settings you can specify maximum resolution sizes for upload and for email - but those are limits on the number of pixels, not the size of the file.
Shal