i do not believe that there will be flood because it is probably a shield world and i am not sure about covenant because as far as i know they went back to their home planets but i definatly believe that you will fight sentinels
well there more than likely is going to be a beta and i bet it will be good and i don think that there will be a beta for the anniversary because its basically the same as Halo: CE and the multiplayer for it is gonna be playable on halo reach if you download the anniversary to you harddrive
well the scarabs wouldn't really work because it would take up too much room and if you want no money or object limit the forge would have to be on another disc so you will have tons of room
well i think that the enemy that you will battle on halo 4 is in fact the sentinels because in the end of halo 3, 343 guilty spark tries to kill you but you end up killing him so once you do that the sentinels attack you and they become a enemy