You can use IIS server as dispatcher but not as AEM server. AEM comes with default jetty servlet engine but you can use other servlet engines/application servers like tomcat and IBM websphere. For more info follow this link. AEM will be hosted either in cloud or on-perm based on the licensing model you have, in either of cases you can access the servers to edit content from the internet but if you would like to restrict you can handle this using whitelisting domain or IP's.
Not really necessary, it should work fine if they have a running browser like chrome/firefox/edge.