Mark,
Regarding the dates of baptisms, in the RC faith, baptism is almost invariably within a few days of birth. The reasoning being that if the child were to die without being baptised it might end up in limbo. Most Protestant denominations take a different theological view and so there isn’t the same urgency. Typically, baptism in the Church of Ireland is between 1 week and 3 months after birth but I have seen many where it’s been years after and, as I have said, batch baptisms of 2, 3 or 4 children of differing ages together are surprisingly common. So you need to search several years after the date of birth (which might not be that accurate either).
Yes there are plenty of records for Aghalurcher. At least 3 of the Church of Ireland churches within the parish have records for the period you are interested in. I have worked with the Aghalurcher registers and know that you will find pages that are torn, pages faded to blank because the Minister didn’t use very good ink, and some entries that are simply illegible. So there are gaps and you won't always find every baptism. As far as finding the records on-line, some churches records haven’t made it on to any on-line sites at all.
According to my guide to Church of Ireland records, the originals of these Aghalurcher registers (which might be slightly more legible) are still held by the respective Rectors/Vicars for each of the 3 churches. You can contact them and ask for assistance. If you go in person and search yourself, I think they charge £12 (sterling) an hour for access or, if the Rector does the research himself/herself, it’s around £19 an hour. But they don’t have to agree to do it, and many won’t. (They get rather a lot of genealogical enquiries, usually more than they can handle). The PRONI microfilm copies would therefore be cheaper (they are free to view) and would have the additional benefit that all the records you need are in the one location.
I had a look at the Muster Rolls for Co. Fermanagh c 1630. There are 2 Storys listed in the county at that period. One was a David Story. He was on the Balfour estate (ie in or near Lisnaskea and Aghalurcher). He had no arms. That is to say no sword, pike, snaphance or caliver. So not very well off. The notes say he lived in Ballybalfour townland. James Balfour of Balfour Castle in Lisnaskea was from Fife, and so some settlers in the area may have come from his estates there.
The other Story in the Muster Rolls was a Robert Story on the Atkinson estate. He too had no arms and so was not very well off. Further away from your family area though.
Stor(e)y is not a very common name anywhere in the UK or Ireland. (Just 18 Storeys in the 1901 census for Fermanagh). In the 1841 Scottish census there were around 123, the English census had about 10 and the Welsh 15. The numbers go up a bit if you widen the spelling parameters but all the same it’s not very common. Mostly focused around the north of England and the south of Scotland. So Border Reiver territory, as you say. Thousands of Reivers were encouraged to settle in Ireland in the 1600s and many made for Fermanagh. Consequently the county is riddled with Scottish border names like Armstrong, Henderson, Hogg, Crichton, Graham and so on. The most common surname in the county is Maguire, a native Irish name. Next is Armstrong.
Regarding how to find male Storeys in Lisnaskea today, I do know of 1. If you go to the UK phone book and search under Storey and BT92 postcode, you should find 3 in Fermanagh. One lives in Lisnaskea (and used to play with my wife when she was a child). You could try him. The other 2 in the county aren’t too far away from Lisnaskea, and could well be related to him. I couldn’t say. But you might want to try them too if they have a willing male DNA volunteer.
http://www.ukphonebook.com
I note what you say regarding having found some of the baptisms in Clones records, and that this might mean the family had moved from Monaghan to Fermanagh. The answer to that is no, they didn’t necessarily move counties. Though Clones town is in Co. Monaghan, the parish of Clones straddles the border between the 2 counties. So someone baptised in the Fermanagh part of Clones would appear in Monaghan records even though they didn’t actually live there. The 3 baptisms you have found were in Tattinbarr. That’s in the Co. Fermanagh part of Clones parish. Aghalurcher and Clones are adjacent parishes. So Tattinbarr and Tullnaharney must be pretty close together. (Tattinbarr is on the southern side of Roslea village, on a minor road leading down to the county border).
However I suspect there are 2 separate families here. The tithe applotment records list a William Storey farming in Tattinbarr in 1832. See:
http://titheapplotmentbooks.nationalarchives.ie/search/tab/home.jsp
Since your William was in NB in 1831, this has to be a separate William Storey, so far as I can see. So a separate family (though possibly related).
We know the Tullnaharney family were in Aghalurcher in 1821, so I would search those records from say 1810 to 1831 to see if there are baptisms for your 8 children (plus the parents marriage too).
You suggest William may have been a tenant farmer. He was almost certainly a tenant. Very few small farmers in Ireland owned their own freehold. (It was a great grievance all through the 1700s and 1800s and a factor in many farmers decision to migrate to lands where they could acquire the freehold). Having said that farmers didn’t move about too much if they could avoid it. Most effective farmers would put a lot of work into improving a farm over a long period of years, so moving around didn’t make good business sense at all. Wasted work. Farmers mostly tried to stay put if they could, but obviously there were times when this wasn’t possible. But you wouldn’t expect them to move very often if they could avoid it. It doesn’t make much commercial sense.
Regarding finding a genealogist to go to PRONI, you could try Historical Research Associates. They have been in business for many years and have a good reputation. But there are others in the Ulster area too if you google for them.
http://www.historicalresearchassociates.com
Let me know if you have any more questions.