Im just a player so I cant 100% answer the Mod related questions but heres my take:

1. Not sure how much mods will look at the seed, but it is necessary to have so that chests can be checked and statue locations to make sure nothing was tampered with

2. I have gotten late enough into a game where my power level and my buddies was strong enough that we could one shot most bosses and keep our structure together but i agree, for general purpose, building is something that hasnt really come to fruition like one might expect.

3. Obamium is actually required for crafting the black sword you get from black gem guardian drops

4. Not sure on this one but I imagine it's just for integrity of the run

5. I love how simple muck is at its core and how memeable it is, but it has elements that make for a very fun speed run. The movement tech and combat is very satisfying to me.

Cheers!