Hey Graham, Welcome to Web Design Talk!
About unlimited bandwidth and disk space, well in the hosting business they truely don't exist. It's a fact. Beleive it or not, there are people out there who can easily use up one terrabyte of bandwidth in a month! And ones who will really use 150 GIG worth of disk space. Most these people have enough sense to know that there's no such thing as unlimited though, but not all of them.
Well are you going to cut them off if they do start using 1 terrabyte of bandwidth a month since you're offering them unlimited? Is your hard drive going to be big enough for them clients that start using 150 Gigs of disk space and all your other clients? I think you can see the point I'm trying to make. You will have no choice, but to cut them off, well letting your server crash continuously may be a second choice.
I would strongly advise against offering unlimited disk space or bandwidth. You'll run into more trouble than it's worth. We'll see what others say about it though.
And by the way you can ask all the questions you want about hosting in the hosting and domains forum if you'd like.
