unless there is some compelling reason you need to play using Steam - and none come to mind - you really should be using Fallout Mod Manager (FOMM) to launch the game using the Fallout Script Extender (FOSE). FOMM makes it easy to remove/deactivate mods in order to diagnose which mods are causing CTD madness so you can ultimately achieve stability.
At this point, however, I'd recommend you suck it up and do a re-install, but with a plan. This is just my method, but I keep a backup copy of the pristine, unadulterated game (literally copy the entire game folder to your backup storage, for example "X:\SteamLibrary\SteamApps\common\Fallout 3 goty") so if there's ever an issue you never have to re-download again. Then be sure to install FOSE and FOMM right off the bat so you can keep a better handle on your mods.
Hope you get it all sorted out, mate...