Congratulations to you for finding something fun to do and makes a little cash! I hope it works out well for you.
You could work with school booster clubs to make the flip flops and they sell them for a fundraiser and you both have a profit. One of the dancer groups at a school here had special flip flops and sold them for $20 a pair. They made money as did the person who made them! PTA's always have fundraisers, sales, etc. Word of mouth is best of course.
Craft fairs and festvals are a great place to go as well.
Now for the business side.... although you are small, you still have to pay taxes. If you collect sales tax you must have a sales tax form from the state.
Your best bet is to talk with a good CPA, find out what is needed per law in your state, give him/her your business plan.
We run our company from home. I manage all the financials which include all the payroll, payroll taxes, IRS monthly taxes, quarterly reporting for the IRS, Workforce Commission, Sales Tax, etc. I have to file a sales tax report and we don't collect sales tax but my sales have to be reported.
Just make sure you get all your t's crossed and i's dotted just right per the IRS so you don't end up owing money, getting audited, etc.
As for a website, we created our own through yahoo and we pay roughly $14 a month to keep it up. Our business is much larger than yours but hey.. everyone starts somewhere!!
Facebook page sounds like a good idea and have friends "like" it.
Best wishes to your success!!