Is 2 hours between train arrival and flight departure (Aer Lingus) to get from the train station to the airport around midday on a Friday by taxi sufficient?
Gare du Nord, actually, but that's only about 500m from Gare de l'Est. The RER train will get you to Roissy-CDG in 45/60 mins, depending on how many stops it makes.
As long as your train gets in on time and you don't have tons of luggage, you should be fine.
Sorry but I don't think so. Security in CDG can be a nightmare and Aer Lingus use T1 which is in itself a total disaster zone. I would leave a minimum 90 mins after arriving at CDG , especially at that time of day. So 2.5 hours from the station would be the min I'd leave.