Hi, I see your thinking of a mod for this - I'm glad someone finally is - and would gladly answer questions on the history of this period.
One thing I did see was your denouncement of both Ireland and Priests, which were both incredibly important in the Civil Wars. To start with, Ireland to the 17th century english is kind of like what Iraq is to us - it was seen as a land of Catholic 'terrorists' who were, alongside Scotland and Spain, the bigget threat to England. The civil war continued here for much longer, and warring started before this, with Strafford succesfully subduing it in the name of the King before being impeached and beheaded by parliament (which created a major rift between the two English factions). Ireland also was a majorly important place for Cromwell to consolidate his power, both militarily and politically.
Secondly, religion was extremely important - one of the reasons that parliament was so keen to rise up was that the Charles' High Anglican preferences and his Catholic wife made most parliamentarians fear a 'Catholic conspiracy' in which the King was in league with the Pope (note this had no basis in fact and was only a rumour). Most englishmen were moderate Protestants, and they saw Catholics as we may see the Taleban; as dangerous and violent religious nutters. This is where Ireland becomes important, as it is a conflict between the English overlords and the Irish catholics. Scotland were Presbyterian (imagine an EXTREME version of puritanism) and so were just as against Catholicism as the English. Also note that Scotland only allied with the parliamentarians after they agreed to change the state religion to presbyterianism (which Cromwell later backed out of). So my suggestion is to keep priests of different christian denominations; although the differences between them may seem slight to us, in their day it would be like comparing Buddhists and Satanists.
However, at the end of the day, whether you choose to use this information or not, good luck
AWZC