Don't view tumblr as a twitter but use it like you would a normal blog.
You can connect a .com to your tumblr and edit the sidebar html to suit your needs.
Make sure to tag your pics and also make sure to add a relevant text below as this goes to the url ending
I have many tumblr accounts and once you have some followers it is easy to grow new ones without much hassle by reblogging your other blogs.
You will soon find communities or relevant interest groups once people start reblogging you.
I have some tumblrs in top google spots with maybe 60k or so followers for all accounts. I follow no one. That is a waste of time and will mess up your dashboard.
The majority of my visitors come from google and facebook, the internal tumblr traffic is just an added bonus.
See
http://www.tumblr.com/explore for some inspiration.
My tumblrs are mainstream, their policy on adult is not that clear and rather random.
Feel free to hit me up if you'd like a few more pointers.