This seems like quite an interesting scenario which unfortunately I don't really know much about. Ignoring the plausibility of the plot succeeding, perhaps someone with a bit more knowledge on the period could answer these questions:
- who else apart from the king and the MPs would be in parliament, and hence blown up?
- did the plotters have any plans beyond blowing up the king?
- what's the likelihood of the plotters being caught? If they are I assume there'll be a massive show trial ending with their execution.
- how bad will the following clamp down on Catholics be? Could this result in revolt in Ireland?
- who would be in control of the regency for the infant King Charles I who was only 6 at the time of the plot?
I think you really need to answer these questions to be able to start drawing up a picture of what the immediate, and more long-term effects of the Gunpowder Plot succeeding would be.
OK, your points in order:
- As well as the King, the Queen and several other members of the Royal Family, the explosion would have also killed the most senior judges in the land, most of the Protestant Aristocracy, most Bishops of the Church of England, the Privy Council and the Members of the Commons. Basically, the entire government of the country.
-The second objective was to head 10 miles north of their midlands base to Warwick, and capture Princess Elizabeth (3rd in line) before placing her on the throne. Charles and Henry would have had undefined duties at court. Henry Percy, Earl of Northumberland, probably becomes protector.
-Though there would be some support in the North, it is very likely that there would have been a counter revolution, a civil war or a Coup d'etat removing the catholics from power. The majority of the population were protestant by now. The plotters would then be exectued in the most grusome way imaginable.
-Expect massive clampdowns on Catholics. In the south, something like 60% may be killed in reprisals or forced abroad. This percentage will be smaller in the north, but actual numbers of catholics dead may be higher. Most of Elizabeth I's moderate policies are dropped, replaced by harsher penalties along the lines of Edward VI. Possibly larger and more extensive plantations in Ireland, so as to create a protestant settled area in both Ulster and Meath, along with parts of Leinster and Munster. Connaught will probably be the only 'Irish' Ireland left. Cultural destruction along the lines of the Highland clearances may be encouraged. Probably large scale Irish emmigration to the continent.
-Not sure about Charle's regent, depends who's left.
As an aside, future colonies will probably be officially Protestant (so Maryland is gone), and there may be less of a crackdown on Puritans.