My idea would be somewhere on the Cross-Border Line, in the mid 90s! At that time, there was a huge variety of stock. For the enterprise alone, you could have DD sets, 201s in IE livery with mk2s, 111s with NIR mk2s or 201s with mk3s push-pulls. You could have some commuter stock, for example, mk3 push-pulls, cravens and arrow units that you were asking about you could still have plenty of freight too. Waterford-Derry timber trains, fertiliser, guiness liners, Bell liners (I think!) and cement bubbles could all still be seen on the line at the time, and could be hauled by 201s, 071s, 141s or 121s 111s would also make a nice change of scene to the IE orange! If you were going to going to model it on somewhere prototypical, Drogheda would be good, as you could also incorporate the Tara mines trains (and possibly the Boyne viaduct!), and if not, then somewhere close to the border would be good. You could have a small loco depot that would locos from the other side of the border and refueling point, some carriage sidings, a cement silo and maybe a container yard if you want!
I did my own plan for the craic, and I think it has a lot of potential A cement silo, some commuter platforms, and mainline platform capable of holding a 201 and 7 mk3 or mk2s, and a loco depot. But it's obviously up to you and depends of your style and taste! You could have a scenic break just above the cement silo with a road bridge or something.
I used anyrail's 50-piece free demo for the plan btw