cardboard VS quilt-serverside-mods

Are you mixing up PaperMC with Fabric? PaperMC indeed is a fork of Spigot that is performance oriented. Fabric is a Modloader just like Forge. Fabric does not have plugin capabilities, since it is Mod based. There are Projects, that aim to add plugins to Fabric, like Cardboard, but these are still a work in progress. As you can see by their Progress Tracker.

I play strictly vanilla Minecraft, and use paper to host my servers, so this may be out of my territory, but I do remember Cauldron being popular for Forge mods and spigot plugins, so maybe give this a go?

The two pinned issues on their github show how much has yet to be implemented. Just as an example, here's the list of events and see how many are unchecked.

I believe it's a mixin conflict between Create and Cardboard: https://github.com/CardboardPowered/cardboard/issues/350

As for Spigot plugins on a Fabric server, Cardboard does work, though it’s still in beta and incomplete.

Use Cardboard: https://github.com/CardboardPowered/cardboard

Some more detail on how the server internals will work: The server is a based on Cardboard which allows both fabric mods and bukkit/spigot plugins to run at the same time, along with datapacks of course. The server has a wide variety of lag reduction and bugfix mods, as well as some rudimentary anticheats to prevent xraying and other blatant unfair advantage hacks

Cardboard exists but from my experience it can be buggy: https://cardboardpowered.org . Use at your own risk!

not a jobs one, no. you can check out the serverside mod list here https://serverside.infra.link/

Have a look at this list. It's got a ton of useful server-side mods which you can use on your server.

To be honest, the natural path for those that come from Bukkit and derivates for the future is to either switch to datapacks, migrate altogether to Bedrock (that already have interesting advances on its addon/pack system) or switch to Fabric server-only mods - There is a lot of possibilities already and there is also Polymer project that aims to "convert" some classic mods to server-side-only, so at the end maybe OP should look at it all and forget the Sponge thing.

This seems like a decent shop mod, for a larger list of mods you can look here. Another shop mod I found was https://modrinth.com/mod/diamond-economy

Once you have your server OS installed, look through the performance section of Quilt Serverside Mods (even though it says Quilt all the mods are Fabric compatible). Also make sure to set sync-chunk-writes to false in your server.properties.

I have been using this list to find some optimization mods but some mods in the performance sections seems to break the game (eg - Very Many Players ).

Here’s a good resource for server-side mods, some of them are for quilt but quite a few are fabric mods (originally the list was only fabric mods, also quilt is a fork of fabric, so if you wanted to give it a go, it has most of the same benefits fabric does)