Should I just register as dba or create an LLC?
The purpose of an LLC is to isolate your personal assets from the liabilities of the business. That is important and you should do it. Using it as a holding company for other businesses is a good idea. Whenever one of the businesses gets big enough to support its own structure, it should have its own LLC. Whenever one of the businesses gets into something that has the potential of betting sued, it should have its own LLC. The purpose of a dba is to comply with local law concerning fictitious business names. A dba is not an entity and cannot protect you from liability.