US citizen with no home state registering an online shop in the US

I am an American citizen living abroad, and plan on starting an online shop selling and delivering physical goods to customers in the US. I have prepared my business plan, but am unsure of how exactly I should register my business. For ease of registration, would you suggest I start as a sole proprietorship in the beginning, then convert to an LLC at the year's end, or start the business as an LLC? And how should I go about obtaining a DBA?

I plan on outsourcing everything I cannot do by myself, therefore having no one working for the company except me, the owner. Therefore, I will have absolutely no physical assets in the US. Where then do I register my online business as being based from?

I understand that my residing outside of the United States, though being an American citizen, complicates the formation and registration procedures for this business. I want to play everything by the book and build this business sky-high, and this means doing things the right way from the ground up. Thank you for your advice!