There’s quite a few alternatives in sponge to those plugins you listed. EssentialsX -> Nucleus, Worldedit -> WorldEdit, McMMO -> AdventureMMO. I’m not entirely sure on what Multiverse was about, from a quick look it seems it was a world management plugin. Nucleus does a fine job of that on its own, though not to the extent it looks that Multiverse had.
EDIT: I can vouch for what @MoseMister said. My first released plugin here was a wild ride as I was learning how to use Sponge, and I was actually also learning Java at that time too which didn’t help with the quality. Think small and expand as you go on.