would it be ok if i played the fallout 3 add ons before i complete the game?

I have beaten the entire game and the thing i love about this game is: you can do practically anything you want..

I would do anchorage first and do the "gary glitch" to get a lot of cool stuff and strong weapons and armor to keep with you for the rest of your game.

I was level 25 when I played Point Lookout and some of the people were hard to kill. I heard from a guy working at my local EB Games that you should wait until Level 30 to play Mothership Zeta because you want to have lots of room in your inventory because the ship has a lot of good things there to take.

Whatever items you get from add-ons carry over to the original gameplay. I did Operation Anchorage at level 10 and got the (can't remember the name offhand) "ninja suit." Then went directly to The Pitt, finished the main mission and got the silenced rifle. If you have good sneakin' skills, the suit makes you virtually invisible to detection and you can take out multiple baddies with the silenced rifle without getting noticed.

I believe you can. I havnt made it that far yet but I have asked my friend who has and he says that you can do so and it will not effect the game what so ever. Its like any add on. It wont effect the game only add more stuff to it.

not at all. just be prepared for a challenge, especially with point lookout. i mean you can't play broken steel until you finish the game anyways so i wouldn't worry about that.

it really doesn't affect the main story the only one you can't play is broken steel,it unlocks once you complete the main story because it continues the story.