Only after completing (yes I said COMPLETING) a few basic games should you start working on something more complex. You could clone some already popular games like the common falling block games or match 3 games. After you have a good grasp of how Construct works, make a few puzzle games. Go through the beginner tutorials and the manual. You can't just start game design with a super complex idea and hope to be successful. Before you attempt any game like HOMM, you need to start with the basics. However, that is definitely not the first game you want to start with.

Yes it is definitely possible to both create a game like Might and Magic and to create randomly generated worlds.