Sailfish OS wiki https://sailfishos.org/wiki/Main_Page
What do the Android app developers need to do get their apps run on Jolla devices / devices based on the Sailfish OS? Many Android(TM) applications will run on Jolla devices unchanged (Android is a trademark of Google Inc.). If you want to take advantage of all UI and other features of Sailfish OS and make yourapplications fast, you can port your applications to native QT/QML. There are extensive guides available on how to do that.
Will you support DRM No.
Will Sailfish SDK be available for Linux and Windows? Yes Sailfish SDK is based on QtCreator and will be available in Windows, Linux and OSX.