If this project is as large as you make out then the platform for it is not really an issue. Whether you use MySQL, PostGres or SQLServer (amongst others) you will want them on their own machine and connect to them via the DBI and the relevant DBD driver (ODBC, PG etc).
As for a scripting language - why not use Perl itself? You can quickly define a set of macros and comeup with an application object that presents a partcular API. Its then trivial to check for bad code, to untaint and to run the app.
Through your API you can also abstract any common tasks and allow the 'programmer' to do stuff quickly and easily.
If you are using Perl because of simplicity and power - why not use it throughout?
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