The EIN and tax information setup are relatively simple steps to take. More important is to have a working relationship with bookkeeping and accounting functions, either by having a bookkeeper or the knowledge to do this yourself.
Also, understand that you're going to need both regular bookkeeping and professional (CPA and so on) accounting advice on taxation. If you want to jump ahead on things, start looking for these services. Interview people, and ask people who they recommend.
If you're not sure, still considering, still working on your business plan, then your time and effort is better spent on the planning than on this red tape detail.
Question added to topic Grow Your Business • February 3, 2009
How soon should I get my EIN and tax information setup?
I am hoping to start my small business within the next year, but am unsure of how early I should get my tax needs taken care of. Will it hurt me if I get the necessary steps taken care of first -- pushing back the store's opening?