Each domain you set up here at dreamhost will be associted with a user. You can set up a differnet user for each domain. With this set up, each user will be totally seperate and seperate from each other.
One user can have multipe domains associated with one user if you want, but no more than one user per domain.
It should be very easy to set it up so your domains are quite seperate from others. I have several personal sites, a church website, and host a few friends. Each has FPT access and shell access to their own domains, but not mine.
As far as a tour of the panel, you should be able to create a web-id for your self - then you can log into the panel. You can click around, though you won’t be able to actually do much with out a plan - but it should give you a good idea.