Some notes on mods and mod managers:

Obligatory: mods aren't supported by iron gate, back up your save often, don't be surprised when mods temporarily break when Valheim updates, Valheim is an early access game, Iron Gate isn't responsible for lost data related to mods.

Aight: Use R2modman instead of Thunderstore Mod Manager. If you search for 'Thunderstore Mod Manager' you're going to be asked to download Overwolf first and Overwolf will run the Thunderstore app. Skip all that, R2modman is the same as Thunderstore without the middle man.

I recommend the Jewelcrafting mod. It's actively supported by its creator and adds a new interesting resources that you can physically collect in the world. It also has a neat 'addon' by a separate creator, Soulcatcher, that lets you collect the souls of fallen creatures and distill them into gems that you socket into your gear for bonuses. It's super neat. I prefer both over epic loot, which is a good mod, but isn't actively supported and its balance is all over the place.

As far as filling in the empty Biomes: Check out the Do_Or_Die mods. They do some or all of that.

You can find links to the mod community discord(s) on most Thunderstore mod pages- it's worth it to check there if you have technical questions or troubleshooting questions about mods as the creators are active on the discord.