Don't have the time to look through all those options right now, but have a look on the "SailRail" website - give it your English origin, Irish destination, dates/times and preferred sea route and it'll figure things out for you:
http://www.sailrail.co.uk/If you play your cards right there are some great deals around. Not sure if the 12-week advance booking window applies to these journeys or not though.
Edited to addYou're probably best off trying to do as much of the rail journey as possible this side of the Irish Sea. Getting round Ireland by train is generally a bit of an arseache, especially since since IE services to Rosslare are dire at best, with connections designed to miss arriving ferries by 5 minutes plus a fairly stiff walk to get to the station. So on that basis I'd recommend Holyhead to Dublin or Dun Laoghaire for the ferry sector.
Putting in the destination as "Dublin City" returns a fare of GBP 63.00 return on your chosen dates (standard class), using the Holyhead ferry.
You can also use the
NRES▸ journey planner to plan a journye to Dublin via Holyhead.
Can't remember if it's Heuston or Connolly that's the relevant Dublin terminus but they're not very far apart. Scratch that, just choose Dublin Port, it's fairly central.