Devkit - Mod Support - Steam workshop

So when I release my game I want to offer some kind of mod support through the Steam workshop what is the simplest way to provide this?

It will be a 3d based game and I'd like all aspects of the game open to modding, I dont mind if they need to use Unity to do so but how would I get my game to recognise the mods and so on, where do I get started?

a nudge in the right direction would be much appreciated as I am finding it hard to find a start point.

at the very least I would like to be able to have custom maps and npc features with modder created scripts, audio, textures and meshes... Maybe even support for total conversions?

I know Ark do this by providing an altered version of UE, can I do the same with Unity? and how would I tie this in with the steam workshop so its easy to download and install and so my game recognises the mods?

I know its not going to be a simple answer.

Cheers!