Your question is a bit confuse.
You mean, is it possible to build up an ADS like server on your linux box, right? ADS (Active Domain Directory) is a Micro$oft tool that keep user/group/user home/program settings on a server. If so :
1- There is no problem using the server as a workstation in a home network. I wouldn't recommand to do that in a production network, but at home, it doesn't really matter, just make sure you won't break anything (i.e.: Don't run the wokstation as root, ever)
2- This is not a stoopid windoze OS. Unless you specifically configure the linux to do it that way, all services will be started on boot.
3- You can configure the server to push the registry (if you are using a windoze client) as well as home. In Unix world all users settings relative to application are stored in the user's home... so...
4- Probably but it wouldn't be a good idea since the last one to log off will probably overwrite the first one applications settings. I never tried this.