Canon: Specific & Vague
When looking at the history of D&D lore on this issue, we have to confront the fact that the majority of sources are nonspecific about how far in the past the uprising took place, apart from noting that the illithid empire was "ancient," as was the uprising.
There is one specific reference, though the number it gives doesn't ...
The relevant book is the 3.x sourcebook The Grand History of the Realms, but unfortunately it doesn't go into much detail on the how, merely that it happened and when.
Their original enslavement comes from the Grand History on page 19:
–8100 DR to –8080 DR
The Mindstalker Wars: The illithids of Oryndoll attack the eastern subkingdoms of Shanatar, ...
Dillard Portyr is Liara Portyr's uncle
The release of the adventure Baldur's Gate: Descent into Avernus has clarified this issue. For example, in chapter 1, the Basilisk Gate section (emphasis mine):
This is also mentioned in other passages of the book, leaving their relationship now clarified.
Based on 3e material, Waterdeep has standing armed forces of nearly 5,000 people
Waterdeep hasn't been examined in great detail by any 5th edition material, but there is plenty to draw on from previous editions. The 3e Forgotten Realms Campaign Setting states that the City of Waterdeep has a population of ~133,000 people, and the wider Waterdhavian region ...