Question about Broken Steel add-on for Fallout 3! ~

I just recently got Fallout 3 (yeah, I'm a bit behind ^^; ) and after.. a couple weeks I guess, I've finished all of the achievement giving/XP giving side quests. I just started the actual main quest and finished The Waters of Life, and in doing so I reached level 18. At this rate I'll reach level 20 before I finish the game - and have wasted XP due to it. If I download Broken Steelbefore I finish the original main quest, will be able to go past level 20 before STARTING Broken Steel? Also, will getting Broken Steel before the other two expansions cause any problems? Or will I be able to get Broken Steel, beat the original quest, go ahead and play the other two add-ons for XP, and then move on to Broken Steel as I'd like to do it?

Sorry if it's a stupid question.
Or phrased in a stupid way, I'm a bit sleepy. =P

Thanks in advance.

yes, you can still get to level 30 before finishing the last non-DLC main quest, take it back!, if thats what you mean.

when you have the DLC just go about your bussiness and after a few minutes there will be a notice telling you the level cap is now 30.