I would have thought that the EMH would have been programmed with aspects from thousands of real Doctors personality's (& some of the creators), rather than the 1000 personality's.
I thought by Zimmerman in DS9 that the EMH had his personality, with a database of MD's knowledge/papers/files.
If they had a thousand personalities it would be a waste of disc space considering the EMH wasn't supposed to be used as more than relief. Also if it were bits of personalities pasted together the EMH's could all end up being psychotic as the Doctor was in the ep I don't remember the name of but he went batshit crazy in.
But thinking too much of Treknology makes me love the other Doctors simplicity. "It goes ding when theres stuff."