Recommendations for Implementation Technologies for POS Application

We are looking into designing and implementing our own in-house point of sale software. We acknowledge that this is a large undertaking, and the specifications are listed below. We are looking for input by developers into which technologies (programming languages, databases, infrastructure, environment) would be most likely suitable for this sort of an application. Our Point of Sale Application would need the following functionality: - Integration with hardware devices (printers, card readers, etc). - "Offline-first" design. The ability to process transactions without an internet connection, however, it can be assumed that the longest period of no internet would be 6 hours. - Used in a desktop (application or web app). - Data synchronized across multiple physical locations. - The ability to expand in the future to iOS or Android Applications for certain features (eg, stock counting) as well. - Stores up to 30,000 inventory items, posts up to 100,000 transactions per year, 50,000 customers accounts. - Application stability & uptime is top priority. - We would prefer for it to be built on some kind of SQL database. The design of this application is still very flexible, as no implementation has occurred. We want your creative ideas as to which technologies would be the best for implementing such an application. Please advise what further information you would like, to submit a written one-page report on the technologies needed to implement. For a suitable candidate, there may be an opportunity to be involved in the development of the application. Thank you for your consideration!