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?