We need to upgrade our current website running just fine on Magento 1.4.1 to the latest stable 1.7.x for future extension compatiblity and possible security issues.
The current website uses some extensions which are mostly upwards compatible with 1.7.x version.
We also have the possibilty to setup a test domain as the sandbox. However, some commercial extensions which use domain sepcific extension keys may not work on the test domain.
Any questions will be answered to the best of our knowledge and we need a developer with plenty of experience doing the upgrades from Magento 1.4.1 with good, verifiable references.