Install and activate (they should be by default anyway) all of them. Broken Steel especially causes crashes if you install it once you hit lvl20. The others it won't make any difference though. But Operation Anchorage in particular is very easy for low level characters but it gives you access to several overpowered items really early in the game and its not a good idea to play it before you hit the lvl20-30 region on a first playthrough. Its better to get to grips with how the game was initially before you get hold of an infinite durability T-51b Power Armour (think the unofficial patch fixed that) or the utterly broken Chinese Stealth Suit.
Point Lookout is a no go area for low levels unless you've already got to grips with the game. The enemies mostly get +x damage boosts to every hit they land which is ridiculous at max level with high damage resistance never mind low level. Entering the mansion primary quest would almost certainly mean you'd never finish it without cheating.
Don't bother with mods (except maybe the Darnified UI) if you've not played it before. Its best to get to grips with the game before you start modding it if only to appreciate what it changes. Plus a lot of the biggest mods change the game quite drastically from vanilla. Once you've got 1 character under your belt just search for the "Best FO3 Mods" thead here somewhere. Things from massive balance overhauls and variations/ additions of enemies to extra areas and modified weather.
