Should be do-able.

No need to reserve in advance, as taxi fares from the parisien airports => city centre are fixed (east or west bank). Note this isn't true in the opposite direction so it will be by the taxi meter.

If your corresponding flight at 13h is within Schengen, I might even think re-arriving back at Roissy 1h30 before departure might be sufficient, as any checked bags get checked to the final destination so it is only a matter of security contrôle.