A few months ago, I installed FO3 GOTY with mods on y computer, but I didn't start playing until recently, but I'm experiencing extreme unstability.
In Springvale Elementary, I have so far crashed 4 times and ad the game freeze 3 times within 5 minutes of playing, so it's more than usual FO3 unstability.

The only wrong thing, I have noticed in the game was a man with a hat and a lot of inventory standing but appearing dead in Springvale (I don't know if that is related).

My modlist is this:

Fallout3.esm
Anchorage.esm
BrokenSteel.esm
ThePitt.esm
PointLookout.esm
Zeta.esm
ArefuExpandedByAzar.esm
Mart's Mutant Mod.esm
COMM.esm
CALIBR.esm
DCInteriors_ComboEdition.esm
Ammo Bench.esm
StreetLights.esm
CRAFT.esm
Selected Containers Respawn.esm
ShadySands.esp
Mole Rat Maze.esp
Xepha's Dynamic Weather - Main.esp
UPP - Quest Perks.esp
UPP - Pack 1.esp
UPP - Pack 2.esp
NotSoFast.esp
HeirApparent.esp
IntoTheDeepWoods.esp
PLweightadjust.esp
rockville.esp
ArefuExpandedByAzar-Radio.esp
CRAFT - Activation Perk.esp
RadiationRevamp.esp
lessviewdistance.esp
NoFastTravel.esp
Selected Containers Respawn.esp
MissingUniqueArmorClothing-Enhanced.esp
FDA1x.esp
FF_WonderMeatMaker.esp
Darkness.esp
CaravanUpgrades.esp
CC.esp
CanterburyCommonsEmbiggened.esp
Project-Valhalla.esp
PreWar Book Titles and Perks.esp
Butcher Petes Meat.esp
Reykjavik.esp
tubRRCompound.esp
RockopolisRebuilt.esp
Wasteland Travel Caravans.esp
Mart's Mutant Mod.esp
Mart's Mutant Mod - Tougher Traders.esp
Mart's Mutant Mod - Zones Respawn.esp
Mart's Mutant Mod - DLC Anchorage.esp
Mart's Mutant Mod - DLC The Pitt.esp
Mart's Mutant Mod - DLC Broken Steel.esp
Mart's Mutant Mod - DLC Point Lookout.esp
Mart's Mutant Mod - DLC Zeta.esp
FasterMorePowerfulMines.esp
StreetLights - Wasteland.esp

Total active plugins: 56
Total plugins: 57

I have tried sorting it manually using fomm and a list I found for Boss, but appeaently something is still wrong. So can anyone suggest, what the problem is?

i know when it comes to the DLC wether they are the actuall ones or something from mods, they need to be in the order in which they were released. So all DLC and DLC mods need to be in the order, Opperation Anchorage, The Pitt, Broken Steel, Point Lookout, and Mothership Zeta.

I tried switching Broken sttel and the pitt to match your suggested loadorder, but that didn't solve the problem, so it must be something else.
All the problems has been in the school, so are there some of my mods which would change anything there. I guess freezes and crashes which returns no errors should be related to scripts (at least I would think so in Morrowind).

Turn off ALL mods except the DLC's and see if it crashes (especially if reproducable in the same spot)
--Turn on half of the mods to see if it crashes
--turn on half of the other half to see if it crashes
--then half of the remaining
and continue to work it to see where the problem might lie.