Bike project 1: Got a line on Baltic birch plywood

I got a line on Baltic birch plywood thanks to a friend of HB's.  Here's the contact info.  It looks like they can provide 5 ply 1/4" at a fairly reasonable price.

The two suppliers in the Boston area that everyone uses are Boulter Plywood in Somerville, Toll Free (888) 9 LUMBER (888) 958 - 6237, www.boulterplywood.com and Downes and Reader in Stoughton, www.downesandreader.com. 

I think I'll give the Somerville bunch a call and drive down.

Meanwhile, I revisiting the issue of wheels.  I've got a set of 20" wheels.  The rear has a 6 speed hub. I'd planned to use a 3 speed crank.  Using the sprockets from the bike here's what I have for available speeds:

The good news is that there are some nice low speed gears.  The bad news is that there are no high speed gears.  I could use a larger crank gear or use an intermediate gear.  A bit of playing with the front gear suggests that an intermediate gear is a better solution.  I'd like the low speed to be somewhere around 2.5mph for hill climbing so I'll need a step down gear of about 1.6 to 1 or so.  I'd like the top speed to be around 25 mph so I'll need a step up gear of around 1 to 2.