Excellent work Igor. I agree with you about the panel lines,; the grain of the wood could either make them look rough, or the engraved line could 'slip' into the grain, making it crooked. On a much larger scale it might work, but too risky on this small scale. The pencil lines will hopefully show through the paint, and maybe you can go over them again, very lightly, once painted.
It's going to look great when finished I think!