No deals for this type of thing, just book as you go - timing it for the sales when they are there ... There's no need to book way in advance (apart from Christmas and the height of summer), just don't leave it to the last minute
You say you're ambivalent between Beauvais and CDG .. I know CDG is awful, but if you're going to and from Central Paris it's a lot handier than Beauvais (and you've a lot more options to get to/from the airport if there's a problem) .. if you have to do the same journey every week you need to minimise the pain as much as possible.
Consider the frequent flyer aspect and lounge access which can be very useful in terms of delays etc... if you're travelling that frequently you should be able to get Gold Circle status on Aer Lingus or equivalent of Air France .. neither are going to be amazing but makes the journey a bit more comfortable if you can use the lounge / priority check in etc.
Also consider the timetable ... Ryanair has only 2 flights a day I think to Beauvais - the flight back looks to be very late at night - that really wouldn't be great ... Air France/Cityjet have the most frequent flights - however with the Cityjet sale by Air France the long term status here may change.