This evening I added a ground plane on the back of the board, which resolved the one unconnected airwire I'd left hanging. I then submitted the board for fabrication by Osh Park by sending them the KiCad PCB file, which avoided generating Gerber files. I've gotten used to submitting Eagle PCB layout files to PCB-Pool so I thought I'd give this a try. It seemed to work just fine.
Although the SOT-23-6 package of the RN4604 dual transistor I'm using as a driver is almost half again bigger than the SOT-363 of the RN4904, it's still a tiny thing with leads spaced only 0.95mm apart. Even building only one of these I wanted a solder stencil. Unlike PCB-Pool, who will provide stainless steel solder stencils for free, Osh Park only does PCB fabrication. So I ordered a polyamide solder stencil from Osh Stencils, which required me to generate Gerbers after all.
One of the options when ordering from Osh Stencils is how big a margin the allow around the board. The default is 1.75 inches, which increased the area from 7 square inches to over 18 sq in and nearly doubled the cost of the stencil. Reducing the margin to the minimum of 0.75 inches reduced the price significantly. Since all the SMDs are in the middle of the board I probably could have saved even more by lying about the dimensions of the board, but it wasn't worth the time.
Later this week I'll place an order from DigiKey for the parts needed to assemble the board. I won't receive the boards for a couple of weeks yet and DigiKey ships very quickly, so there's no rush to do that.