OK so I have fallout 3 GOY with all 5 dlc's on 360. My question is, when do I incorporate the expansions? I'm about 2 or 3 hours in and haven't installed them yet. I'm assuming I should play them near the end/ at the end of the campaign? Is anything retroactive about the expansions?... meaning that if I dont install the 5 dlcs now, i will be excluded from some content..

Go at about 10 hrs.

The only thing that can happen if you don't install the DLC is that if you reach the level cap (which is Level 20 in the original version), you will stop gaining experience. The Broken Steel pack raises the level cap to 30, so you should make sure to install the pack before or as you reach Level 20.
 
VERY MINOR SPOILERS - NOT A BIG DEAL, BUT SOME PEOPLE ARE SENSITIVE - Also, Broken Steel removes the "Point of No Return" from the game, so you can continue your adventures in the Wastes without having to reload a previous save (you wake up a couple of weeks after the events of the end game). So you should aim to have Broken Steel installed before you start to reach the climax of the game. END SPOILERS
 
Aside from that, it doesn't matter when you install them. The other four packs basically just act like sidequests much in the same way as the sidequests in the original game, so you can do them at your discretion.
 
Enjoy!

i'd say level 10

It didn't auto install them all for you? Thats what happend with the PS3 version. Was very funny stepping out in the wastes for the first time and seeing all 5 expansions 'come play me!' messages pop up at once. As for when, I'd say install them all. Then you have a single large world at your own pace.

I say start whenever you feel like it! The DLC's aint all that hard. I'm not sure if I remember this all correctly, but when I started on my second character when the GOTY edition was released I began on the DLC's at once. Mostly because I had already completed the main game. So again, begin whenever you want.
 
Most the DLC's are very good, but the main story is so much better. In my opinion anyways...

they're usually endgame DLCs, since they came out after everyone hit the level cap anyway, but you could concievably to it at around the level 10 mark if you're a combat focused character.

I picked up Point Lookout when it went on sale, and I started exploring that area this past weekend with my Level 11 character, and it is not easy. At least make sure you're well equipped with some above-average armor before you take that boat trip.

" I picked up Point Lookout when it went on sale, and I started exploring that area this past weekend with my Level 11 character, and it is not easy. At least make sure you're well equipped with some above-average armor before you take that boat trip. "

I was wondering this too since I've started playing the game on PC.  I never got too far on the 360 but am having a blast on PC now.  Anyway, I too have the GOTY edition but I think I might keep the DLC content for my second play through although I might install Broken Steel if I don't finish the main quest before level 20.

start 'em whenever.  I've played through that game 3 times and twice I have started the DLC missions immediately upon getting out of the vault.  Oh, and the armor from Operation Anchorage is incredibly good and will make the rest of the game way easier.