1. Age of Ice has a Sub-forum in the forum, and may theoretically be updated there eventually. However, currently it has only been updated in official BtS patches.
2. After the current phase, Shadow, is complete he will go on to Ice, which will consist mostly of scenarios (don't know how many) but also some tweaks to the game to make the scenarios possible. The fact that it will also include the fleshing out of the Illian civ has lead many to think that in at least one of these scenarios you play as Auric Ulvin trying to regain his godhood, and to plunge creation into another Age of Ice.
3. No, .31 will still be Shadow. There have been many bugs reported in .30, so when Kael gets around to solving them he releases a patch. Of course, on his machine he is working on a later version of the mod, so he goes ahead and includes some of the new content he has recently added too. .31 was supposed to have been released over a moth ago, but Kael figured that most of us would prefer smaller downloads and so has just included all of its additions so far in patches. I'm hoping he will keep doing so until he has finished the Hinterland and Morale mechanics. There will probably be at least 4 versions of Shadow before Ice, which probably won't be released until at lest this summer or fall.
4. There is a sub-forum for maps, scenarios and modmods (I myself am making one of these, but haven;t had time to work on my second version). In the past the team has borrowed some from other modmods (Maniac's and Sureshot's mostly), but not extensively. I'm not sure about the non-FfH fantasy mods. I know FfH has borrowed graphics from some of them, but that is mostly because a team member was working on both projects (several members are part of multiple teams, especially the art guys)
5. If civ released another patch, then FfH would probably need at least another patch too. They are usually designed so that you can still play pre-patch games after the patch, but not vice versa. However, as a BtS Beta tester Kael gets those patches before the rest of us. In the case of the 3.13 patch, Kael made FfH compatible with 3.13 about a month before the official patch was released.
6. I can't speak for the team, and you would probably have to ask each member individually anyway, as some may be too busy. I do know that they wouldn't mind if the Arda mod borrowed code from FfH, or even used FfH as its basis and proceeded like a modmod from there.