Ok....have just begun playing FO3 on XBox for the first time (and love it) after playing FONV for the first time this past summer (and loved that game as well). I bought the GOTY version and I am currently on level 8 and will install all the DLC's probably before level 9. I have read almost all of the insightful topics concerning 'when' one should start to play each DLC. I have decided to do OA before level 10, then Pitt around level 12-13, then PL around 15-16 (will do MZ sometime after level 20).
I really would like a 'somewhat' simple answer to when I should begin Broken Steel? I know that it will add an extra 10 levels to the game (as well as extending gameplay forever).

I would like to know if doing the BS add-on 'before' level 20 and then completing it 'before' level 20 actually goes to the endgame when you complete level 20? or does it allow you to continue to the end of BS if you start BS after level 20 and complete it then? I guess (from what I have read) there are two 'different' endgame scenarios. One for the original endgame (no DLC's), then one for completing the BS dlc afterwards. I don't want any 'spoilers' per say....since I have read about the plausiblity/non-plausibilty of the two different endgames without actually knowing how the endgame finishes. Just need some guidance on how to proceed and enjoy 'not' knowing how either endgames conclude.

(btw...the FO series are the best games I have ever played and love how one can just explore forever, while also taking your time to complete the MQ's at your leisure).
Thanks in advance.......