Looking great so far!

I'm sure you have already thought of most of these, but here's a couple of suggestions: (having built a few myself)
1. Remove the motor until after you've covered it(and fuel proofed the firewall), so that you don't get balsa dust & yucky stuff into the motor
2. Use tri-stock epoxied on the backside of the firewall in the corners to reinforce it
3. Also use tri-stock under the horizontal stab when you get to that step, to give it more surface area to attach to
4. Before you cover it, sand, sand, and sand some more. Use progressively finer grit, say 150, 240, 400 or so. It makes the covering look much better.
5. Build a small hatch into the bottom of the fuel tank compt. for the battery, that's where mine usually end up after trimming and balancing. If you do this during the build, it makes it a lot easier later on

Good luck, post more pix as the build continues!