You've done a Kickstarter so presumably you know this, but to reiterate: I would be very, -very- wary of offering rewards that might result in shipping out a bunch of stuff, because shipping is a) time-consuming and b) unpredictably costly. $10/mo seems really low for getting a physical book once a quarter.

(I'm in Canada and also in a tiny apartment, so I'm not in for More Physical Stuff regardless, but.)