As a note, all of these activities have been leaked already through
destinytracker.com's database, it's just now that we know it is partially on disc. What's even worse is that you are able to glitch yourself into some of these places on Earth and see enemies in them.
The first DLC will include 4-5 missions, 2 strikes(one on earth, one on Mars), 1 raid(on Moon) and 3 crucible maps.
Second DLC there is less details but I assume again 4-5 missions, 2 strikes, and 1 raid(which takes place in the reef)