Opening an online shop is not as simple as it might first appear. Apart from having an attractive website that shows your stock to best advantage, and allows your customers to shop quickly and with confidence, you have other considerations that are at least as important.
To name but a few:
Warehousing and stock control; shipping procedures; accounting integration with existing systems; terms and conditions of sale and returns; legal disclaimers; compliance with trading standards; CRM policies; SSL Certification; etc, etc.
Massmedia can advise you and give examples based on their experience in online commerce.