[Should i make part mods?]

You know how they say Rome wasn't built in a day? The same principle applies to modding things.

No one can tell you what you should do; that decision is entirely up to you. However, starting small and building up piece by piece may be better than jumping in the deep end. Or for a more contemporary simile:

Sure, you can try to learn calculus without knowing algebra, but it's like building a house on sand.

[How would modders feel about posting to Nexus Mods?]

Nexus Mods? Oh, heck no. I'd rather eat a cactus. I've been there before and trust me, it's nasty.

[KSP 2 Modding Wiki]

I was just Googling KSP 2 API to see if documentation existed (like KSP 1's) and this is the post I come across...

Y'all are magical, I swear. 

[Any Documentation on sound modding?]

I don't think there's any documentation for the API itself yet, and from what I've seen mods use BepinEx to load themselves in-game.

With that being said I suppose you could use BepinEx or Harmony library/loader to make a mod that plays music  at certain points. It would be messy, but it could work.

[[1.12.x] Revamped Eeloo! New Moons and Atmosphere!!]

Very nice! I'll try it out but it looks cool. Eeloo is long overdue for some attention IMO.