@Lee I can help with the Bible download issue for version 2.4.6. Just let me know what Bible you want to use and from what website and I can create the required file...same as the wizard would do. If you are having issues getting the specific verses from a web Bible, I suggest using the Advanced search to select the Book, Chapter and verses and not use the normal search. We are getting near a release of the next version of OpenLP that should fix the issue found in version 2.4.6, but the latest beta version has a bug that prevents it's use by most users...so we wait for the next release!
I am not sure about the files download from OpenLP. If you are talking about exports from OpenLP or service files, you should be safe to archive them offline without any trouble. After 6 years you could have a lot of stuff in your OpenLP databases. This could cause a bit of time to find what you are looking for when building a new service. You could backup your Data directory and then clean out the different libraries to remove items that are no longer used. The backup would make the cleanup safer because you could switch back to the backup if you cleanup too much!
There should not be any reason OpenLP should slow down the device it is running on unless the device is low on space. If you need to archive the source files that get loaded into OpenLP, be sure to save the path to the source files. Version 2.4.6 is able to handle source files that disappear to some extent. The upgrade to the new version when it comes out may not be as forgiving!