Valhelsia Structures seems like a great surface structure mod to go in the pack, considering it adds new structures like houses and graveyards to explore and loot.

OK.

Fins and Tails should absolutely not be added, there's already way too many aquatic creatures. Upgrade Aquatic, Alex's Mobs, Quark all add new aquatic creatures. Plus none of the mobs from Fins and Tails have interesting mechanics.

Valhelsia Structures theoretically could be added, but blockswap would be needed to fix Quark overlap.

Edited it to not have Fins and Tails being included