How many would you say in need to know i already have about 8 learned off is that enough ?
you should see which ones came up last year(renaissance writer, leader of a revolution, archaeoligist,settler during a plantation and a leader in the fight for irish independance) and rule these out. the same p.i.h. have never come up two years in a row. As far as I can tell the p.i.h. show no pattern other than that. However, it seems quite likely that the following will come up, however it is not guaranteed. you should know 9-12 p.i.h if you want to be safe.
~an artist OUTSIDE italy during the renaissance(rembrandt,durer)
~an irish political leader(john.a.costello)
~a religious reformer(martin luther, john knox/calvin)
~a leader of a voyage(colombus)
other likely ones to come up/important ones include:
~early christian monk
~soldier on d-day/german soldier on operation barbarossa
~factory/mine owner during industrial revolution
~irish person during the emergency
If you pick around 10 to learn you should be fine