Yes, you can host as many domains (or sub-domains) as required. Each will have it's own web accessable directory with the same name as the domain.
For example, if you had the domains xxx.com and yyy.com, you would have the following directories in your home directory;
DreamHost use their own home-grown admin panel. While it does take some getting used to, especially if you are coming from a host that uses cPanel, I find it provides all the functionality you could want.
You can create new WEBIDs (panel log-ins) and set certain privileges for those WEBIDs, limiting what each has access to in the panel.
Yes, I believe you can create a DreamHost account (without purchasing any hosting) at the link below;
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