The last time I checked, only the host needed the mods and the rest was good to go.

Originally posted by Jctkd1:

I will host the server, ...
...
We are using a Gportal server at the moment.

Those two statements can't be true at the same time.
Either you're hosting it or they are (=you're just paying).
Anyone of you got an internet connection with >20Mbit/s upstream? I recommend hosting it yourself[valheim.fandom.com]

Originally posted by Jctkd1:

If I download mods, will my friends also need to download them or can they just log onto the server and the mods will be there for them and usable.
I know that V+ can be turned on and anyone on the server will be able to play it with V+ and the settings that have been chosen.

Have you read any of the mods manuals/documentations? Many have specific sections on server stuff/requirements/options.

I'm using ~18 mods and almost all are client side (only). Only one (NoAFKEvents.dll) is server+client side.
Dunno about VH+ or "Odin plus mods" but so far I haven't seen any server-side-only mods.

Originally posted by Jctkd1:

... and they are automatically there for anyone that joins the server, or would all my friends need to download them also?

Usually everyone needs to have the mods too. I recommend stuffing them in your personal modpack (just a 7z archive with everything required = bepinex, mods, configs).

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Originally posted by Judge Shredd:

The last time I checked, only the host needed the mods and the rest was good to go.

Where did you check that?

Originally posted by L1m3r:

Usually everyone needs to have the mods too. I recommend stuffing them in your personal modpack (just a 7z archive with everything required = bepinex, mods, configs).

If you use R2modman for installing and tweaking mods, you don't need to bother with making a modpack. You can share your profile code and other players just need to make a profile with your code. They will get all the mods you use + all the settings you changed.

@OP: having mods on the server requires a lot of work. If you don't have previous experience it would be the best that you find someone who will navigate you through the whole process. It will require a lot of your time, and every time you want to update mods or add another one you will need to go through the same process again.
As L1m3r suggested, maybe you should think about hosting it yourself rather than using gportal because it will be a lot easier to add/remove mods.
On my last modded server i spent more time tweaking and testing mods than actually playing the game. If you plan to combine Epic loot mod with some of Odin plus mods, you will definitely need some tweaking and testing.