1. NXT stands for 'next' actually, just a little name I use myself.
2. Templates as they are now will be removed. In NXT you can create templates yourself, just arrange a few smart object and save the template. Then you can share the file online, that way many templates can be created by users.
3. Yes, it'll contain a few smart objects to create buttons. If you've got a configuration you like, you can save it as a template.
4. Nope it's not, those will probably be scrapped depending on how fast NXT progresses.
5. Currently Kenney Studio will remain at 0.5 and NXT will be added as a separate download. NXT will have active production until all features have been ported, then NXT 1.0 will be released.