And you checked that it is not already registered in your state?
There is a link to the trademark site in the left column on the forum... just go there. There will be alot of information regarding how and when to apply for your TM.
You could go with Sole Proprietor as well. My advice would be to contact 2 resources: your local Small Business Development Center (just google that name and find your local outreach on that website.) They can help you entirely with every aspect of set up and growth, and it is already paid for with your tax dollars and waiting for you to use it. There is no additional cost to you. 2. A local accountant. They can help you figure out what is right for you as well. The SBDC can help you with that, too. Both can help you find out about local taxes you may need to sign up for as well.
Please do a search on the forum for "legalzoom". You will find threads from users who liked using them, but you will find more threads about how legalzoom basically offers a service that you can do for yourself on your state's Business Website. Instead of paying Legalzoom to fill out the info, you fill it out and only pay what the fee is for registering or for a ficticious name if you need one. Much cheaper. Also, faster according to some unhappy Legalzoom users.
If your business name is not registered by another company and the dot com is available, get the dot com as soon as possible. Going with someone like Godaddy, you can get the dot com for $10 for the year... you don't have to host it yet, but get your dot com as quickly as you can. I search the company name I want, if it's available, I search the dot com, and grab both in the same night!
If you don't have to, you don't want to be the dot net of your company name, or have to add hyphens, etc.