Since you plan to biamp and have some eq available via the sub amps, you can use as narrow baffle as you wish, strictly speaking. But, there are certainly trade-offs -- as the baffle gets more and more narrow, you'll need to add more and more eq, taxing both the amplifer and driver. Off the cuff, I don't think you'd want something more narrow than 24" or so, generally. Maybe 18" but that's definitely pushing it.
10" drivers are generally on the small side displacement-wise. If you haven't yet purchased them, you might consider the 15" Auggies. Certainly people have had good luck with one of the 15" per side on a narrow baffle. If it were up to me, I'd prefer to see 2x15" per side. I would think the Reckhorn won't have any issues with the 4ohm load, and the additional displacement is a nice thing. I have a relatively small room, 13'x18', and I don't feel the 2x15" AE OB15 per side are overkill at all.
Regards,
John