Lucky you to be visiting IOM--I hope to do so myself someday.
Judging from what others have said, if time is limited on IOM then it is best to spend the time touring the island, getting immersed in the culture, etc. rather than trying to examine records that usually can be done elsewhere.
As Frances said, the parish records, wills, etc are all on microfilm and available via the Mormons as well as in official record repositories.
Have you discussed your lines with the genealogists here on this bb to check out some of your data?
Good luck in your endeavors.
Donna