zilav

BSAs can't override each other in Fallout 3, this feature was added only in Skyrim. Previous games require custom xSE extensions to implement that. For New Vegas this is done by JIP LN NVSE extension (read about .override files) https://geckwiki.com/index.php/BSA_Files#Notes_2 No idea if something similar exists for Fallout 3.

Can't be fixed unless someone will manually readjust positions of troublesome cliff refs in the entire worldspace (there is a mod for that for Skyrim). And even then it will lessen z-fighting, not remove it completely.

Regenerate terrain LOD https://stepmodifications.org/forum/topic/13451-xlodgen-terrain-lod-beta-85-for-fnv-fo3-fo4-fo4vr-tes5-sse-tes5vr-enderal-enderalse/

xDump, you'll have to compile it yourself or ask someone in xEdit discord https://github.com/TES5Edit/TES5Edit

2GB for games prior to Fallout 4. Unlimited (technically) in Fallout 4.

This is an engine bug when LOD doesn't switch off up close. The selected object is not LOD but the fully loaded mesh for which the LOD got "stuck".

Objects LOD consists of merged macromeshes covering 4x4, 8x8 and 16x16 cells depending on distance, there are no separate objects and hence nothing to select. No idea what screenshots you've seen, but it was not selected LOD for sure.

-32767..32768

No, you can't.

Use xLODGen version from the STEP forum, generate LOD4 terrain meshes with quality=0.

Use hex editor to replace a single letter like "BstomaCompanion.esp" for example in the plugin's header, create an empty plugin with the same name to server as a fake master.

"Is it really THAT hard to just duplicate a worldspace with EVERYTHING in it?" Yes, everything involving a new worldspace creation (either from scratch or duplication) is one of the hardest tasks. You can't just copy worldspace in xEdit and expect it to work as is. This requires a lot of additional clean up postprocessing by someone who knows very well how the engine works.

It does, but it works in the UI thread. So if your system suspends UI of background apps for whatever reason then it will stop obviously.

Yes.

These are Editor IDs of sound records (descriptors) in plugins.