The blockers are that would take the entire modmaking community to work at it for three years.

A purely Lord of the Rings campaign is out of the question, but you could certainly do a pseudo fantasy themed campaign.

Crossbows and close combat weapons are easy, coming from Dark Souls, Star Wars, and Skyrim weapon and armor mods/ghost templates. There's plenty of melee focused custom classes too. Shout-out to the old Dark Souls weapon mod allowing the crossbows to have their own separate stats you can edit, such as damage or clip size and a further shout out to one of the Star Wars weapon mods (at work, can't check my folder) that gives Force Push and Force Lightning as assault rifle and pistol options, complete with unique animation

There's more fantasy style armor choices if you search around the workshop too, such as from Fortnite

As for magic, you'll have to use psionic abilities. Luckily, there's plenty of custom classes that not only have them from the start, but variations with elemental damage too. The Necromancer custom class also includes a "magic staff" weapon you can allow on other classes if you edit the files.

You can use the elf head mod for basic elves, and because it allows more colorful skin tones, you can use it for orcs too. If that's still not enough, you could consider some of the Star Wars head mods for more fantasy races.

If music is your thing, you could look into the Fire Emblem or Nier music packs.

You imagination will have to fill in all the rest of the blanks, except for the Sean Bean voice pack.