There's a discussion topic on this at airliners.net
FCO Possible New Base For Easyjet? — Civil Aviation Forum | Airliners.net
The original source is in Italian at:
[ANTEPRIMA] Richieste di slot per la base easyJet a FCO - I forum di Aviazione Civile
Summary from thread says:
FCO-MXP 5 daily
FCO-PMO 2 daily
FCO-CTA 3 daily
FCO-BRI 2 daily
FCO-VCE 2 daily
FCO-VRN 2 daily
FCO-TRN 2 daily
FCO-CDG 4 daily
FCO-ORY 2 daily
FCO-SXF 1 daily
FCO-LGW 3 daily
FCO-MAD 1 daily
Some of the above routes are flown to CIA instead. Assuming these get moved to FCO, a rough calculation says they will need about 4 or maybe 5 planes to be based in Rome.