Hi,
1. I plan to build a Site Provisioning system at some point probably as an add on product that can allow users to provision their own sites with an option for ecommerce so one could sell sites, but not sure how soon that feature will be available, not in the next few months for sure. So, yes its possible but no we don't have this yet. Currently only admins in the root site can create new sites, it does create a default admin@admin.com user, and you can configure some files to make some default pages/content that will be created for new sites.
2. I've never setup 2000 sites on a single installation but in theory, its just a matter of whether the site has the resources to handle the aggregate traffic. From IIS point of view its just one site. 2000 low traffic sites is equivalent to less sites with more traffic.
There is a file in the root named mojoSiteMap.config, in the current release its only configured for up to 100 sites, but recently in svn I bumped it up to 200. It has to be configured for up to max number of sites you plan to host. Its just a config file that hooks up the correct site map for each site, it has entries like this:
add name="mojosite96" type="mojoPortal.Web.mojoSiteMapProvider" securityTrimmingEnabled="false" />
<add name="mojosite97" type="mojoPortal.Web.mojoSiteMapProvider" securityTrimmingEnabled="false" />
<add name="mojosite98" type="mojoPortal.Web.mojoSiteMapProvider" securityTrimmingEnabled="false" />
<add name="mojosite99" type="mojoPortal.Web.mojoSiteMapProvider" securityTrimmingEnabled="false" />
<add name="mojosite100" type="mojoPortal.Web.mojoSiteMapProvider" securityTrimmingEnabled="false" />
so to go up to 2000 sites you'd have to keep incrementing and copy pasting until you get to 2000 or whatever your upper limit is planned at. The numbers correspond to SiteID.
Hope it helps,
Joe