I think that the distributor will tell you what format you should use and which DRM you have to use.
If you don't have a distributor, you may have a problem, as you have to pay yourself the licence fees for DRM (if required in your particular case), and find a place where to store your book to be accessible from the eReaders (those with access to libraries and shops).
A hot issue is the embedding of fonts should you need to do this, because your project is commercial and many otherwise free fonts might require a licence fee.
Not easy, but if you'd go the other way, non-DRM, you may not have customers
