Need help with 7 day itinerary in Ireland

Don't be too surprised that any responder will want to know "what you like". They (we) also want to know if it's seven days or nights, and whether it includes travel days, where you're coming from and if it's your first visit, and importantly, what time of year.

Unless you manage to get a lot of sleep on a long-haul flight or are very experienced with driving on the wrong side, your travel day over is best spent in Dublin, with maybe enough energy left to visit a nice pub.

If it's your first trip to Ireland, you need to limit the areas you want to visit. You could easily spend 7 days in just Belfast and Dublin, but you'll entirely miss the Ireland "experience". Northern Ireland and a few towns in NW Ireland (Donegal, Westport, Galway, etc.) will gobble up your time. You can skip NI and hit Galway/Clare/Cork. Doing too much is fine if you don't vacation to relax. We tend to jam-pack our Ireland time, but we're retired and spend our normal life walking in the forest, so relaxation isn't our goal. We've also been in Ireland for eight weeks over three trips, and have no end in sight. I have detailed plans for two more three week trips. Don't underestimate the size of Ireland.

"Don't be too surprised that any responder will want to know "what you like". They (we) also want to know if it's seven days or nights, and whether it includes travel days, where you're coming from and if it's your first visit, and importantly, what time of year."

We'll be coming from Seattle. 2 days of travel (1 at the beginning and one at the end to go to our next stop to England). It will be our very first time. The time of year will be mid-September. My daughter and I don't need to pack out our days and definitely get a feel of Ireland and don't need to spend a huge amount of time in the cities.

I wouldn't fly into Belfast as it has no flights from outside Europe- so you would have to fly via a hub airport in Europe or the UK. Given the high frequency bus service from Dublin airport to Belfast (at least 3 per hour with the various companies) that doesn't make sense.

There are also buses from DUB to Donegal and Derry/Londonderry so you could easily do a west and north coast circuit ending in Ulster and get back to DUB with ease.

Not sure what you mean by the Antrim Islands- there is only one which you can access- Rathlin (from Ballycastle). I would argue that is certainly worthwhile and ideally with an overnight stay. But whether that is best use of limited time for a first time visitor is questionable.

There are buses along the wonderful coast- but along the most scenic eastern part they only really work in summer peak season. It's not impossible at other times but is slow going with several connections.

So outside of high summer I would do Belfast then to Ballycastle, along to Carrick-a-Rede, Bushmills and the Giants Causeway then Derry then into the Republic. In a week I think you'd be hard pressed to then get south of Sligo (in the Republic) for buses (direct to DUB airport) and trains to Dublin.

You have a hard choice to make whether to include or exclude Northern Ireland, or just stay in the Republic- then even then very hard choices as to where to go in the Republic as you can't possibly cover the whole country (or even all the key sites) in that time.

We've decided to stay 13 nights in Ireland in Sept 07-21st.
With more days/nights, there's more time to see different parts of Ireland.

-If we want to visit the Western areas Ireland, is it better to rent a car or use bus/train system?
-Is it advisable to make reservations for pensiones or hotels or can we reserve just in time (2-3 days before)?
-Does anyone have any recommendations for "adult hostel or pensiones"? What city or town is it located in?

Car or public transport? A lot depends on where you want to go and what you want to do once there. Many people have enjoyed a holiday using public transport to get around. This works well for the main tourist areas/sights but if you are wanting to get off the beaten track and away from the tourists, a car is a definite advantage.

September misses the worst of the peak holiday crowds but is still a popular time to visit. Most people do book well in advance now rather than 2-3 days ahead. Many places will already be fully booked.

In places with lots of accommodation, you can probably find somewhere at 2-3 days notice but don't rely on it. You may well end up not where you want to be, paying substantially more for accommodation or ending up in places others don't want to stop. The days of B&B signs hung out on the gatepost are long gone and many smaller places that used to put up a sign during the summer months have disappeared.

Without a car you need to use the larger towns as bases in order to make use of the guided day tours to get to some of the sights you will want to see. The four that I used were Dublin, Killarney, Galway and Belfast. Of these four, Killarney takes the longest to get to by train or bus, and once there it is difficult, and time consuming to get to Galway. You could spend four nights in each of Dublin, Galway and Belfast and see quite a bit without a car, but you wouldn’t get down to Dingle or the Ring of Kerry if those were places that interest you. You could also start in Dublin, do a couple day tours from there, train to Galway and rent a car from there to travel down the west side to Dingle, then back up to Dublin airport to fly out. I would check what the fees are to drop off the car at a different location, though, as sometimes it’s quite expensive. I would suggest looking at tour company itineraries that are a similar number of days, and see where they go. Maybe you could rent a car and follow an itinerary of a tour that goes where you want to go.

I'm making my fourth trip to Ireland this summer. First two, someone else mostly drove. The little bit of driving I had to do was a nightmare. This time, no car. We'll mostly be in the North and NW, in areas where you typically "have to" have a car. The cost of renting a car there is enormous, and I expect to pay less overall for transportation, even though I will be using a taxi/private driver on at least two days. Worth it to me.
Don't let anyone talk you out of flying into Belfast. My best advice is to get yourself over the ocean in whatever way is best for you (cheapest, shortest, most legroom, whatever your needs are), then you can connect from there. Of course, there are direct SEA-DUB flights that can be very reasonable. I will be flying in a lie-flat seat SEA-Frankfurt because it's lie-flat and I could pay for it with (lots of) miles. So I decided to spend 3 days in Germany before flying into, you guessed it, Belfast.
Definitely book ahead what you're able to. The long-distance trains in the republic are bookable ahead at a discount. NI trains, not.