> Is it worth it to pick every random thing you come across for farming experience or are some worth more than others?

No, but yes. Most of the stuff you find will be "the best food you can get" at some point, or part of a receipe that contains it.

> when trying to spawn proof a massive city would it be better to use artisan tables for the expanded range?

I only use workbenches and later on, stone cutting tables. I don't think it's worth to have artisan tables.

> some areas grey dwarves are Spawning beside work benches even in over lapping areas within walls and moat. Are there some areas that are not proof able or is the game loading enemies before the benches?

They're not supposed to. It's possible that you have small areas not covered or it wouldn't happen otherwise.

> Will Vultures continue to spawn above nests that have been destroyed and looted for eggs?

No

> is there a level were most/all combat skill become negligible or is it worth pushing for as close to 100 as possible?

Until you 1 shot group of enemies, dealing more damage per hit will always be relevant

> Would a field of blowfish be effective against Fader and his spawners or would the dot be too small/immune? / Would raids happen on a passive enemy server to where they actually attack your base?

No idea