If you are going to be using Twitter to market your handmade business, your username should reflect your business name. Meaning, it should be as close as possible to your actual business name. For instance, ours is @daft_crafts. My personal account, for my business Lu & Ed, is @lu_and_ed. This helps make it easy for people to find your shop - if they see you mention you have a Storenvy or Etsy shop, if they browse those sites with your username, your shop will come up. And you definitely want to make it as easy as possible for people to search for and find your shop!
Avoid obscure Twitter names with initials and numbers - get it as close to your actual business name as possible. The beauty of Twitter is you can change your username at any time without losing any followers, so if you need to update your name to reflect your business it is a seamless process. Just make sure to make an announcement to let people know you've changed your username!
You are allowed to have a username up to 15 characters long, but the shorter the username, the easier it is for people to retweet your tweets and reply to you with more characters to work with since Twitter only allows 140 character messages.
Is the username for your business taken? Add underscores to separate words in your user name or add 'shop' - IE, if you wanted to get, say, @wildrose, but that username is taken, try @wildroseshop or @wild_rose or @wild_rose_shop - just don't compromise on your business name being a part of your username!