1: the only real limit on shared hosting is CPU time, others here can explain it better than I so I'll let them chime in, but yes you can add unlimited domains to your shared hosting account.
2: yes you can add all those emails (unlimited). Dreamhost email servers are different than the web servers, so you don't need to worry.
Also please don't spam the forum. You have posted your request on several existing threads, which is not only unnecessary, it's also rude. Once is enough, in your own thread. If your unsure which section to post in then take your best guess and post ONCE, it will get answered even if it's mis-categorized. This forum isn't very large I'm sure most of us being helpful use one of the two links in the top left corner.