It's going to take you forever to develop such a system. Why not buy one off the shelf?
Anyways, In terms of development platform, all languages are good. It's the coder that makes the difference. There are some language which are more flexible yes, but it really depends on the features you plan to implement. If you are looking for a RAD platform (rapid application development) then I suggest Visual Basic. As for the Database, due to the large amount of transactions you will have, you definitely need a powerfull relational system. Microsoft SQL Server is great and has tons of features, while still keeping decent performance. In terms of operating systems, If you use Visual Basic and MSSQL, then evidently you want to go with Microsoft Windows (2000,XP). That way you keep all technologies in the same page.
One thing I tell you: you will run into hell when the time comes to synchronze the transactions... he he, not an easy task when you have a lot of them and different stores to take care of.... thats why I suggest you buy an application off the shelf. We sell some interesting ones, including a POS solution that is currently in use by KINKO's (1,500+ store chain). IF you want more details in such a system, check this out:
http://www.akaconsulting.com/infotouch.asp
Any questions or comments, please DO NOT reject my answer, e-mail me first at juanja01@optonline.net
(rejections hurt my ratings :)
Good Luck!
