wow lots of questions! Well it looks like a lot have been taken care of. A great place to get just about all of them answered is the feature list for OS4 on the Amiga.com site. If its not working you can do a google search and find it at a few other sites IIRC.
My understanding is the first release will be a lot like 3.9 only on the PPC systems. All the stuff like MUI ect is built in and fully working. No limits or keys required ect. The USB will be handled by a custom stack made for OS4. Its not following the Poseiden stack like MOS has done. The TCP/IP stuff is also a new custom stack called roadshow. from what I have seen its quite nice and should work well. Video modes as far as I can see will be a new Picasso96 system and use a lot of modern video cards, with even more to come as mentioned. Its looking to be a great OS.
