First, please use our own installation guides at Installation - diaspora* project wiki, other guides are sometimes pretty outdated.
And I still don’t understand why you want to re-install diaspora on a new server, when the title here says you want to connect with tumblr which you can just do on your existing pod. If you need help with moving your pod to a new server, that would be a completely different topic. And the most important point with this is, that if you want to re-install/move your pod that should run on the same domain again, you would need to import the database of your existing pod instead of
db:create which creates a new empty database which then would break federation with all usernames that already existed in the database of the existing pod.
So please tell what exactly you have done and what you are trying to do, but so far the thing don’t make a lot of sense. Again, “connecting with tumblr” and “re-install/migrate to a new server” are two completely different things.