I don't think the window would be a problem. I think your mare would have to try
to get a hoof through there.
I really like those stall fronts. The swingy bar part is smart.
As far as the price, I think it's just a little steep. $3300 for three stalls... not that would know the average price for a stall front.
Have you planned the rest of the barn? That's my favorite part.
Are you planning on having solid partitions between the stalls?
Will the stalls be slightly sunken? (I know at the barn where I do stalls, it would be a huge pain with all the sawdust coming out from under the door all the time if they weren't lower than the aisle.)
Speaking of aisles, how wide?
Any special flooring (ie rubber bricks) to go over the cement floor?
Automatic or manual waterers?
I'm kind of pressed for time right now but good luck on your barn!