How would I create a Bitcoin tumbler ? Is it legal to have one as long as it would only be used for legal transactions? What would I need to start?
What do you mean by a Bitcoin tumbler? Is it an object that holds water? Or any other thing? I'm confused.

How would I create a Bitcoin tumbler ? Is it legal to have one as long as it would only be used for legal transactions? What would I need to start?
bitcoin tumbler for what purpose you will create, what you want ask or it is just typo mistake?
I think he means tumblr. You can start one. You won't need any requirements.
Unless you mean a mixer, I think it is legal bit you'd need a lot of capital.