Commuting from Europe - free if in uniform as stated above. Just need to ask for
JS from captain. Can bid for overnights to minimise time in Ireland although will be at the mercy of the roster gods and relying on swapping with other pilots if you end up with a roster full of early start Dublin duties. Likely you would need to either get a B&B in Dublin for a few nights a week at a minimum. Need to consider being rested before duties as well and the weather gods may not always play their part so you shouldnt be cutting it that fine on your commuting plans.
LHS progression is nowhere like 20 years as stated by the idiot above. 2-3 years has seen some of the more recent joiners onto the 330 which makes commuting much more bearable. Commands currently around the 10 year mark. Have been lower during periods of expansion and management tell us that it will drop below the 10 years significantly with the planned Atlantic expansion. In anycase sitting in the RHS of a 330 going across the pond once a week is probably the best gig in the airline so I wouldnt see it as a negative waiting your turn according to seniority.
The lack of DECs is a positive. If you want a DEC then you need to go and prostitute yourself somewhere else.