You don't need a DBA for your domain name as long as you are charging people based on your LLC name. Once I got my LLC I did a DBA because I wanted to charge under a different name for different part of my business.
As an example you can have Jason Glib LLC. and the Site myawesomebusiness.com. When people buy stuff off of myawesomebusiness.com you charge them from Jason Glib LLC. As a courtesy just tell them you are charging from that name.
I set my business start date as the next day after I got my confirmation certificate. other than that I have no idea.
p.s. all the "no legal advice" boilerplate applies here.
no you do not need a DBA for your website so long as none of your sales/customer contracts use the website name.
As for business start date it can be when you make your first transaction and receive revenue (or hired an employee or signed shareholders contracts - basically anything that constitues "business activity" which varies from state to state, but typically incorporation/LLC formation alone isn't sufficient to trigger it). The business start date is typically used by States to determine when taxes apply to your business - best to defer this as long as possible, but usually it doesn't matter unless you incorporated at the end of the tax year and started making money during the subsequent tax year. In some states you will still have to pay the minimum franchise tax for simply having a business entity regardless of when you start making revenue.
Disclaimer: This is not legal advice and does not constitute an attorney-client relationship.
Agreed, but be sure to ALWAYS use your LLC name in connection with your website name when doing business. you need the DBA only if you use the website name separately. This varies by state though- I'd look up the local rules- look up "Certificate of Assumed Name" or the like for your state.