I think zagiace was advising him based on these two lines; "Do I have to do anything differently on income tax forms after filling this out? " and "Ok cool so I don't have to do anything as of now except that form? Good to know it's legit!". Not specifically on the W9 issue which was also included in his post, which I agree there is nothing further needed for that.
But, yes, there many be things you "need to do differently on income tax forms after filling that out". For one, you many need to fill out state tax forms for collection of sales tax. You many need to file quarterly income tax forms depending on your income level. it may be advisable to change how you file your income tax forms. Once you start selling products your tax status changes, and you are required by law to jump through extra hoops.
Fill out the W9 yes, but before you start selling anything you are well advised to seek out an accountant or tax professional for advice. Not doing so can be very costly when the IRS, state, or local tax authorities start to add on penalties, fines, and interest, because of innocent mistakes. And no, they don't accept "But I assumed...., or I didn't know..." when it comes to settling the fines.
You are crossing the line from a individual paying taxes, to a business. Whole different set of rules. And absolutely, lots of things you need to do differently on your income tax forms!