Large tumbler

Go with steel, not plastic. With all the weight, the rocks will grind through the plastic barrel rapidly.

I posted a tread on my using a steel cement mixer for tumbling not too long ago. I have a lot of really rough chalcedony I tumble this way in particular as it rapidly cleans the stones and removes all the sharp edges. The weight significantly increases the grinding rate.

Once they are too a certain point, I remove the rocks that have finished enough that I can decide whether they go in to the smaller tumbler, get slabbed, broken up, etc.

I also posted my other observations, including the sand and mud settles to the back eventually locking the smaller stones in place so they cannot tumble. Therefore, it is very important to routinely remove this sediment.