Hello Jacquesdp1, I'm doing something very similar. Instead of converting Datasheets (XSLX, XLS or whatever) i'm extracting/converting data from an old Informix database, and uploading data into Oracle database. I'm an Oracle expert, having 20 years of experience. I can only help you if you are willing to do it with Oracle platform, no matter operating system, Windows, Linux, etc..
The Informix-Oracle migration I'm performing, is a Government Organissation in my country, Argentina, I can provide you with emails if you need to ask for references.
Also, part of this migration is being made by uploading Exell files from other Government Organisations into the brand new Oracle database.
User interface for access the new Oracle system is being made by me, using Oracle APEX, this will allow the end users to log into database using web browsers so they can do reports, pie graph, flash embedded app, etc...
It is not easy, I've been part of this migration for the last 6 months. Still in the middle of the process, the Organization won't stop the actual Informix production system until all the code have been migrated.
That's all.
Best regards