IC / AC differences

Well, when it comes to new boats, apart from the extra rag ICs are now built to a box rule, whereas the ACs are built to a one design shape that was also used for ICs between the 1970s and a few years ago.

The box rule boats tend to be a bit thinner and are quite a lot lighter. They also tend to have rather finer bows.

Build - well same as any other high performance boat really. The weight limit is readily achieved for the AC, but quite challenging for an IC, especially a wooden one, although I haven't heard of anyone missing the minimum by enough to matter. Although the plank looks a bit intimidating there's plenty of help available - even, I think, a CAD drawing to get a sheet of ply laser cut into a plank kit.
Pro built shells for home completion are readily available for both ICs (Bloodaxe, to a choice of designs) and ICs (Razorback boats).