Another reason to use/install the latest version(s) of software especially when upgrading from software that old with so many changes in base coding likely.
With regards to the above discussion, one would want to evaluate what specific impact does each of the 25 modules have on successful purchasing and what of those are just extra baggage. Beyond that, the coding philosophy and principles have changed since then, just because there is not an identified error, does not mean that the code is "sound" for future use... Would also suggest rebuilding your configure.php files to approximate what is provided as a demo configure.php file named (or closely named) dist-configure.php. Just to be sure that defines such as DIR_FS_LOGS is included in loading and logging of errors in the /logs directory.