You can have one file for everything, you just specify the xml file and pick "re-use existing" when you setup configs. But then you wont get the option to setup anything specific to that package. Additional configs or changes need to be done by editiing the file.

In our old setup (pre-2012 stuff) we use SQL configs (same as xml 1 table = 1 file) with one table being dedicated to all connection mangers, file, FTP, OLE, ADO, Caches, etc.... anything that could be a source or destination. we have a few hundred entries in that table and its a standard config in every package. We then have a single SQL config table for every solution or project, these at a minimum all have 1 entry called ApplicationName which is the name of the solution or project (used in standard error message). I would recommend against i config per package, that will become difficult to manage very quickly.

hth Tom