I was wondering about the same things because for me as a rather new player sieges are really annoying, I already have enough FUN getting my fortress running without them...
As for 1) : in the long run you will want to be independent of surface-level wood anyways. Because you will reach the point where you already harvested most if not all of the trees - especially when you need them for charcoal as long as you donīt have access to coal or d magma. My strategies for that are:
- Only use wood where it is absolutely necessary. This means beds, bins and maybe charcoal.
- If possible buy bins, chests, barrels, buckets etc from traders and focus your production on stone goods to exchange for them.
- Buy logs from elves.
As for 2) : I donīt think itīs possible to completely automate the process of letting in migrants and traders safely. I guess you *could* try to arrange a complex system of pressure plates connected to which try to channel dwarf migrants into a meeting hall inside your fortress, but that wouldnīt account for the pets they bring and for the other races the traders can have. As for traders I donīt think it would be possible at all since they need direct access to the depot upon arrival. I was hinted that using bridges is relatively save against invaders. And that you can disable them completely in the .ini file.