The LT-40 was my first build too, and despite my many 'learning experiences' it flies beautifully!

I know what you mean about the shear webs too, as I went through exactly the same thing as you're doing now. The shear webs/rib positioning always seemed a little 'off' from the plans, so I fastidiously shimmed the shear-webbing with slivers of balsa to get everything aligned perfectly with the plans. It wasn't until my second kit that I found out that plans change size due to temperature and humidity, and you should instead position the ribs according to the size of the shear-webs Shimming the shear webs isn't going to hurt, especially if you make sure that you get the shims glued in good and tight, but it isn't really necessary.

Good luck,
Neil.