Were there any proper B sides for this album, and if not, was it the only Genesis album without any?
Well, GENESIS was the only Genesis studio album of the post-Gabriel years not to have any associated non-album B-sides. There weren't all that many non-album tracks released in the Gabriel era, of which some were A-sides rather than B-sides, and not all the albums had any associated with them.
The only studio leftover was “A Call To Arms”, which Mike subsequently used on the first Mike & the Mechanics album. Details here (look in the “Background and recording” section) :
It's a stretch calling ACTA a "studio leftover" since it was just a "bit" that Mike and his co-writers built a song around, rather than an actual leftover song, as some seem to think is was. (I've read a professional review of the first M+M album where the writer assumed that Tony Banks wrote the lyrics to ACTA.)