You will also need to learn a few PHP script if you want to use Content Management System (CMS) like Drupal or Joomla. For blog you can use Wordpress. I even use Wordpress in some of my website.
Now, what’s the advantage if you learn web design? In my case some of my clients who outsource their programming job (desktop programming) sometimes needs a website. So instead of referring another programmer to handle the job you can grab it and earn another income.
We cannot anticipate what our clients need and it’s very important to learn in advance before the demands come. But see’s to it that you have one language to master. Mastering just one language should be your foundation. Although it is okay to have a general knowledge about other languages but in my experience it is better to have one primary language.
It is sometimes advantageous to your client if you suggest an Affordable Web Hosting. So your client will think that you have a good intention in helping them. Sometimes we cannot be a good programmer if our attitude towards our client is negative. They are the one who gives us money in return of the program or source code.