A dba filing in a county in New York State protects your name in that county only. A corporation's dba filing with the Division of Corporations in New York State Secretary of State office protects you in the entire state.
A DBA doesn't protect your personal assets, it's just a fancier way of doing busines so your sol proprietorship sounds bigger, but it won't protect you from creditors.
A viable and available trademark should only be chosen after consultation with counsel, sice the fees and non-refundable and it takes 4-6 months, minimum to find out if you'll even have a successful application since about 1/2 of all applications get rejected by the USPTO. There are also state TMs, and that might be appropriate, depending on the kind of business you've got in mind.
A domain name can function as a trademark too, and that, like the TM itself, needs to be chosen carefully.
No matter how much reading you've done, it's no substitute for the advice of qualified lawyer helping you. A little investment in legal work now will be well worth your while.
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An attorney in IA would be best able to answer your question, but if you can afford it, an LLC would best protect your interests in my opinion.
A DBA is just a name for a sole proprietor to use instead of their personal name, you can get checks make with your DBA on the check, but there is no limitation on liability, so any expenses are yours personally.
A federal trademark is something that you put on goods and services, and is different than a DBA, you cannot get checks issued with a trademark as your name.
An LLC is a separate legal person from you. Bank accounts, credit cards, loans, and other contracts can be created in the LLC's name. If your LLC goes bankrupt, that does not mean you personally go bankrupt. The LLC limits the liability of the members of the LLC to the amount of money they invest in the LLC. It comes with responsibilities like, you cannot pay for personal things from LLC bank accounts.
An attorney in your area would be better able to explain to you all the pros and cons.