Few answers
1. Mendix 4 is unsupported. The first major supported version is 7.x, which will probably be dropped in a year. So, if you want to use it as a mendix app, strong advice to upgrade
2. Consuming data from that mx app database can be done by exposing webservices. In newer mx versions, rest and oData are supported out of the box
3. If you aren't using the app anymore, just the data. I would consider migrating your data to a postgress db of your own.