Ahh... feeling good. Got a biogas setup going, and even with a solid heat generator it doesn't burn through fuel nearly as fast, nor wastes potential energy like a steam boiler. Also got around the problem of charcoal.
Protip: If there's not enough room for a large tree farm, then make a large tree farm. That is, instead of a tree farm that covers a large area, make a farm for large trees. Firs are massive and easy to cut down with a treecapitating GT axe, and Rainbow Eucalyptus, while a little trickier to cut down due to the branches spreading everywhere, but are far easier to find since they grow everywhere. In both of these cases, you'll get 3.5-4 stacks of logs from just one tree.
And yes, modded logs/planks do seem to work with GT tools and machines.