Absence of records before 1750

I have been researching my ancestry through Ancestry.com for the past 8 years (with several stops and starts), and discovered six different bloodlines that originate or pass through Ireland.  My DNA test pretty much confirms this, since it estimated that I am 32% Irish.  However, the most recent birth of any of my Irish-born ancestors was 1718, and all six bloodlines last have births in Ireland during the period from 1680 to 1718.  

From what I see on this website, it appears that most Irish historical records (birth, marriage, baptism) do not go back beyond 1750.  Am I correct to presume that I am at dead-ends on these bloodlines?  If so, I would be interested in closing out these lines of research with a more general history that studies what it would have been like to live in Ireland at the time of my ancestors.  For instance, for John Jameson (my 7th great grandfather) I would like to know:

1. Why might his family have immigrated to Ireland from Alloa in Clackmannon, Scotland to the County Galway just prior to John's birth in 1680?

2. What would life have been like for John and his family in Galway:  what was the population and the demographics of the area, were there any significant events in the area at that time, were there famous people who might have lived there at the same time. etc.?

3. How and why would they most likely have emigrated to the United States around 1720?  Are there records of ships that would have taken people to America?  Was the Colony of Pennsylvania (where John eventually settled) known to be recruiting settlers from Ireland around that time?  

Any tips on how I might start this type of research?  My wife and I are going to be visiting Galway on August 25-26 as part of our first trip to Ireland, so I'm trying to learn what I can before the trip.  

Thanks so much.  

Mark

Dallas, Texas