BBoostr is a great service for running more than just a few tumblr blogs, one of the main reasons is that it takes all of ten seconds to export the queue of a blog you already have and import it into a new blog in the same niche. I recommend you spend your time filling the queue with as many posts from as many different blogs as possible first, this way you get varied queues that attract viewers more than just reblogging from three or five blogs all the time.
After that you go to your queue in Bboostr and click the export button, save the queue to a folder of your choice (tip: Google Drive folder to allow backup and also working from everywhere you might be).
After that just go to your new blog’s queue (likely to be empty) and press the button to the left of the export button, select your file and upload it. Don’t forget to shuffle the queue with the button to the far left!