Hi Scouser, Lets start with quetsion 2... try using a tarp instead of cutting so much wood! I know we've all seen R.M. with a lovely solid shelter built of about half a ton of pine trunks, and we've sen the design in all the books... Trouble is we just don't live in the sort of landscape that will support this sort of destruction in the name of Bushcraft. If you want to build a shelter with minimal gear, try getting hold of something like one of the ex-army tarps (basha) or treat yourself to a Tatonka tarp. Even one of those cheap green plastics sheets they sell at B+Q with eyelets round the edge. These will take up little space in a pack (if packed well), weight is minimal, and yet they will allow you to build a waterproof shelter almost anywhere in a very short time. Team the tarp (or plastic sheet) up with a handful of paracord and you'll be amazed at just how many designs you can come up with for your shelter that involve cutting little if any wood.
Building a decent shelter in this country at this time of year using only "natural" materials can be a real pain in the you-know-what. We have very few plants that have leaves big enough to make the job easy at the best of times, but in Winter the options are almost nil. As you have found, cutting enough wood to effectively build a log cabin roof is just a waste of energy and a waste of trees. It will probably end up leaking like a sieve anyway....
As to the best place to find dry firewood, almost anywhere you find wet logs will do IF you look at those wet logs differently. Split a wet log down the centre and you will as often as not find that the wood in the middle is still dry. Split off the wood from all around a big fat dead wet log and you'll often be surprised at how much good solid dry wood there is in the middle.
Even in our lovely British climate you can often find nice dry kindling twigs if you look under a dense evergreen like a yew tree or a pine. You can find dry tinder inside the split trunks of old trees too. Wood that has been hung out to dry for you by nature is always useful. Keep an eye out for dead wood still in the trees. Firewood gathered from on the ground will almost always be damp, but dead wood snapped from a living tree does it no harm and the wood is usually much drier. Dead branches that have already snapped off by the wind etc but have got hung up in the tree are ideal to use.
PLEASE don't go felling trees willy-nilly to make big solid shelters without the express permission of the landowners to do so. The ideal scenario for a bushcrafter is that he/she can camp somewhere for a couple of nights then move on leaving virtually no sign at all that they were ever there.A few days for vegetation to spring back into place and a shower of rain should cover all signs that you were ever there at all. A trail of felled trees and what others would see as mini log-cabins will only lead to bushcrafters in general being seen as desructive woodland hooligans by those that manage our forests and own the land.
Keep your fire small and scatter the well wetted ashes too. This will not only prevent accidental fires but prevents there being a series of fire scars being left along your trails in your wake.