WillowsTree

I would stray away from stuff that adds a buttload of surface structures. In my experience, while fun, they give you waaaay too much stuff. The only essential mod that I have is CarryOn, but I have really enjoyed my time with Toolsmith, which adds things like custom handles and bindings for tools that can give better durability or speed, as well as sharpness to tool heads to also increase their speed. If you don't put thought into tools with Toolsmith it will be a pain in the rear, since at base a stick and base head is a horrible tool, but if you put the time into getting even a decent handle and binding you can go a lot further than in vanilla.