Having some trouble setting up mods for my new server

[DelBreck]

Hi. I've decided to put a server online in anticipation of H&H coming out soon.
I've secured a provider, logged in, and even gotten my world loaded.

I'd like to include mods on my server, but I'm having some trouble.
The first thing I was told is "Start with Valheim+," which I do not wish to do (I use BepInEx directly, through Vortex, rather than VH+).
The tech trying to assist me through the Provider's system could not make it work (possibly because my own understanding of the process is limited)

Are there any tutorials, tools, etc for either setting up mods on a server, or on how to build a modpack myself?
(I tried googling making a modpack, but the only instructions I could find relied on Thunderstore and were therefore zero help)

Thanks for your interest