So I'm thinking about playing through Fallout 3 again. I'd like to add some mods. But there are so many mods available that I have no idea what does what, or which works with which. Hopefully somebody knows what I need and is feeling charitable.

What I'm looking for is to make the game more immersive survival-wise, and more sane shooter-wise. So. I think I need to start with Fallout Wanderer's Edition for the first. Does it add uses for random salvage in the wastes? Does it have a better sense of having to MacGuyver your way around shortages and hazards? And I need a mod that makes combat sensible (no shooting people with 100 rounds of 5.56mm to bring them down) and doesn't add utterly insane levels of difficulty (die after two hits) or silliness (no fantasy-RPG weapons etc). I like gun porm but it has to be gritty and dark and wastelandy.

I am prepared to offer 5 pounds of clean rice and a tool sharpening kit for advice.

Yeah, FWE does all that. The entire aim of the mod is to provide an immersive and harsh Wasteland feel.
Best take a look at the mods description, it is one of the biggest overhauls afterall

It's definitly aimed towards core-players that really want to get immersed into the game.

Sounds like FWE will suit you nicely. The great thing too about FWE is that if you do find some aspects too easy or too hard for your liking you can adjust most of those settings in game. As for gun porm you can check out my weapon mods on FO3Nexus in my sig, they all now have FWE patches too.