Hi,
 
Im quite far into the original fallout 3, 94 hours to be exact with a lot left to discover but I have hit the level cap. As such my question was when should I install the DLC because as far as I'm aware Broken Steel raises the cap to 30 and I don't want to lose the XP I could be earning now however I hear it also drastically increases the difficulty of the game with the new characters and 3Dog gives away some of the story. In which order should I play them and when?
 
S

I played the DLC after I beat the game.

I installed the DLC after I finished the game.  It does add a new (tough) super mutant type person but I'm not sure they show up in all areas or just the new ones.  Not that it mattered since I almost never died in that game.  The only must have expansion is Broken Steel, because it allows you to raise the level cap.  It also continues the story immediately after the end of the regular campaign.

There seems to be ONE radio glitch with Three-dog and it's nothing game ruining:
 

Well definently get broken steel right away if only because at level 28 you can get every location in the game marked on your map which makes it a lot easier to get all of the bobbleheads and just so you can be absolutely sure you've seen everything.

If you don't want to install Broken Steel on a second playthrough, just start the final mission, install it, and once you get a message saying the caps been raised complete the mission. Three Dog does actually give away the ending during one of his broadcasts.

Thanks for the advice people. I think i'll install the DLC and just keep the radio off until i've finished the original main storyline. Keep getting sidetracked though in my attempt to completely explore the map.