Airedale260 has already answered the 1st point. It was only really under the latter Stewards that large numbers of Scottish Presbyterians were settled in Ulster.
Parliament's importance was because it held the purse strings. That's what Charles wanted to crush it and remove any restrictions on his ability to raise taxes. The Dutch and the British were bitter rivals economically, hence the
1st-Anglo-Dutch_Wars, in 1652-54. I think your thinking of under William and Mary who deposed James II in 1688-89.
Actually Charles II did take part in two more wars with the Dutch, but the 3rd one was more motivated by his secret treaty with Louis XIV. Which was to partition the Netherlands but more importantly for Charles would ensure a regular subsidy from Louis which he hoped would make him independent of Parliament. Fortunately this failed as the Dutch successful managed to defeat the Anglo-French attack as it could have been disasterous for both Britain [autocratic monarchy restored] and Europe [neither Britain nor the Netherlands in a position to oppose Louis's schemes for wider conquests.]
Its a distinct danger but he failed to conquer Scotland before. Also even if he wins quickly, heavy taxes without any restraint is likely to cause continued dissent in England. Which might mean another rebellion against his rule. This could end up failing but its not certain.
Given his character I can't see see Charles letting Ireland go either. Its part of his kingdom by divine right - at least as far as he's concerned. Also unlike his son's who in exile became favourable to Catholicism he's still very much a Protestant. As such an independent Catholic Ireland, even if not involved in pirate attacks on shipping, would be too great a threat to Britain. Teh basic reason why Britain felt it had to hold Ireland.
He would definitely be more interesting in Scotland. I suspect that at least the 1st refugees would go to the continent 1st and probably few making the long trip across the Atlantic. Also S'task probably covers this better than I could with his comment above.
Because it makes a victory by Charles far more likely. As such then a very nasty period of totalitarian autocracy which could last several generations unless you get a more long sighted monarch or a bloody revolution, French style.
Airedale260 raises a good point about the Ironsides and more generally the NMA [New Modern Army] but those took time to be organised and trained and were a response to early defeats and the flaws of the Parliamentary forces. In a scenario with Polish help they might not have time to do such.
You do raise a point about the Polish nobles thinking of their state as a aristocratic republic but that might not be a significant factor, especially since the Polish king might be unwilling to send such people with the force. [And also Charles wouldn't want people who might find things in common with the people he was seeking to suppress.]
Anyway hope the above answer's your points.
Steve