There is no limit for number of devices to run Keepmark for a single license.
No. Currently Keepmark is a desktop application. However, documents are stored in a user-accessible form and can be synchronized with mobile devices, e.g., using services like Drobox or the WebDav protocol.
You will find a short guide how to configure workspace synchronization in the attached video.
See attached video to see how to configure email account in Keepmark.