Very cool, so make sure you take the tip of the mecurial branch default.
1) Thread sort based on last post date as you see on http://orchard.codeplex.com/discussions/topics/5240/core
This is already implemented - I think its the default - Ordered by published date.
2) A category View (might be a widget) with last post snippet as on http://orchard.codeplex.com/discussions ..
You can do this with projections, I have added a category and tags to the Forum and the thread so should be really easy to do.