Radars don't need to be located at current stations. They can be anywhere. That opens up a lot more possible locations, unless we get the usual nimbysm like we have with the wind farms. But from that list, certainly Waterford and Donegal Airports are most needed. Others would be south Kerry/west Cork, Belmullet/Mace Head and somewhere like Mullingar.
I suspect they are counting on the radar systems in Wales and Cornwall to cover the SE. Coastal locations west of Cork and south of Donegal would seem to be the most attractive in terms of maximum range. After that it is down to spacing between them (assuming there will be more than one), proximity to service personnel, good road access, terrain type (avoiding mountains is hard in the inland direction!) and availability of a good (3 phase?) power supply.