I heard they are initially basing 3 airbuses at this new base.
No there will only be 2 new A320s for the new base.
1. LONDON HEATHROW - It would take one of these all day to operate back and forward to LHR plus one other aircraft for a rotation if say they were to have 6 per day. This route is a winner, would say its already making BD nervious about there Belfast Heathrow link (rumours of talk with BFS). Aer Lingus have experience of this exact route/competition at Dublin.
LHR is key. A BFS base will almost definitely not be set up if the can't get a codeshare with BA for LHR. However there is the small problem of slots. I heard before that they have slots leased out, so perhaps these could be used, or a rotation dropped from the underperforming Shannon route. 6 flights per day is highly unlikely, they simply would not be able to get their hands on that many slots. However they would need to get the agreement of the Irish Government for any change in use of the slots.
Personally I'd tip BHX for the new base. It has a lot less competition than BFS and a much better and more affluent catchment area. They could operate routes to Madrid, Berlin, Venice, Vienna etc. where there are currently no competitors as well as operating the flights to Dublin and Cork which are currently operated by Dublin/Cork based aircraft. Lots of Northern Ireland travellers travel via Dublin anyway (over 1 million per year according to Wikipedia), so if they just advertised more in the North they could probably attract more people to travel via Dublin without actually setting up a base in Belfast.