I did the ubuntu install as well. The only thing I had to do differently was use 1 name and not the whole name.
Yes, you can use a made up name, make sure any routers that you use are using dns relay so that you do not get some bill collectors at your door for it ( just joking..) anyway, you can put what ever you want for a name.
I used: "Server" and nothing more for mine, it worked great! But, you may want to get a domain if your running this type of server in general, it was designed to control a domain much like an ISP's setup.