I agree with the others who say you should take your Meteor, the bike you know and trust!
The Danube route is a bit hilly at first, but levels off when the cycle route follows the river more closely, it presents no real climbs that would warrant buying a bike just for that tour. .
Whilst cycling the Danube you will see quite a variety of bikes, and have the opportunity to speak to other tourers which may help you to decide which bike you might get next.
PS It's not just in Ireland that few bike shops cater for tourers
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