If lots of data sources are open on start up and they are causing InDesign to become slow or inresponsive the InDesign Preferences may need resetting. The easiest way to reset everything is to delete the InDesign preferences: as soon as InDesign starts to boot hold down Shift, Alt, Ctrl (and Apple/Cmd if working on a Macintosh). A dialog will appear asking to delete the InDesign Preferences, select ‘Yes’ on this dialog.
In EasyCatalog, using the close button in the corner of the panel will hide it; to close the panel completely select ‘Close Panel’ from the EasyCatalog Pop Out Menu. When the panel is only hidden its data source will still be loaded at startup.