2. How would you handle the possibility/risk of making Steam achievements that later become obsolete or nonsensical/impossible to achieve due to design/mechanical changes in updates?
Maybe they'd just be meta-achievements than anything in game consequetial or over-intrusive.
Complete the tutorial, embark for the first time, play for 1000 hours probably.
4. Why are there only mammal and reptile werebeasts? Was this a design decision, or just about not having time or interest to manually hardcode loads of bird and insect werebeasts and instead waiting for them to be generatable?
Probably for ease of handling additional limbs (which Toady wants to approach more into the Magic or future arcs, in dealing with mutative effects, growing a extra arm and such due to magical exposure etc.) that make avian or spindly invertibrate creatures hard to pull off without keeping a human profile (and no great increase to size), as well as the additional abilities they could hold.
A moat might tide off a were-zebra (maybe not were-hippopotamus) but a were-octopus would probably building destroy all your aquatic floodgates into your fort as a 8 armed menace, GCS web throwers are hard enough, as are flying enemies difficult to deal with. At least having additional tags would probably mean they would be a rarer caste, which casts shadows over creatures such as minotaurs not being a challenge by comparison.
5. How do you manage doing bugfix updates/patches for current versions, while still working on large changes that are not ready to be released to the public (that is, getting the bugfixes/patches in both the release, and in the unreleased version)? I only ask because I wonder how that's possible to practically manage without using a version control system or branches (assuming that hasn't changed).
6. Related to the last thing, how do you keep track of what changes you have made to the codebase and to features?
Last i remember on a similar set of questions, the Tarn brothers have private note-lists of suggestions to draw upon at a later date and also
the public development log. I dont think its a excel spreadsheet or anything a technical as that.
I couldnt possibly speculate on that, DF can already be translated into github files (infact quite a lot of it being retrieved is central to the DFhack project), but maybe there's a alternative arrangement in place.