Having a good looking Tumblr will let your followers know that you mean business. The layout is important because you are mixing pictures and words throughout your page. Premium and free themes may exist that have the look and feel you want, but you just need to find them. There are plenty of themes you can pick and choose from if you please. Sometimes a theme will have just the structure you want, but it needs modification for the colors or branding you’d like to use.
If you know how to modify and replace graphics yourself, this can be easily done. The key difference that you must accept if you want to blog using Tumblr and not WordPress is that you won’t have the concept of “plug-ins” – they don’t exist on Tumblr. So anything “extra” added to a theme, will have to be added to your Tumblr theme code as raw code, meaning you should only then edit it if you know something about how to do it without erasing the style of your whole Tumblr. To import your HTML into your custom theme you will need to login and select the appropriate blog on the left sidebar inside the Settings section of the dashboard. Look for the Heading titled Theme and click the Customize button. And this can get very difficult, so make sure you look up how to HTML before hand.
When deciding on a URL, make sure it is a very easy to remember URL. You put it at the end of Tumblr dot com. If it’s easy, your followers will remember it, and it will make getting new users easy. Don’t use too many colors or different fonts. This could draw the unneeded attention to other parts of your layout that is not the main focus.