Tis probably wrong to reply to my own thread, but I've done a bit more digging and have stumbled upon
the facility of an "apex_collection" to cache my dashboard data, so that sounds promising.
Also, the problem with the nonfunctioning query might have something to do with not being granted privileges, but
I will either dig deeper or perhaps avoid this with the apex_collections.
Anyone care to confirm whether these suggestions might prove fruitful?
Thanks in advance.
external tables are a good device for staging data to bring into the database, but not a good idea for running your application from directly. I would load this data into the database before querying for the application. apex_collection is good for caching session dependent data, but will require to be refreshed for each session.