I just found this thread and thought I might chime in.
I have been having an 'off forum' discussion with another member in regard to Harquebusiers. Some of the info we have been trading might be of some use to others of you.
It states: "At the beginning of the Civil War in 1642 English cavalry, also known simply as “Horse”, had developed into two main types. The rarer “Cuirassier” was the last relic of medieval times being almost completely dressed in armour including, in some cases, a fully-enclosed helmet. However the expense of maintaining a unit of Cuirassiers was considerable and few units were formed.
By far the most common type of English Civil War horse on both sides was the "Harquebusier", a medium cavalry man dressed in a tough buff leather coat and lightly-armoured with a helmet, back and breast plate."
“conscribe te militem in legionibus. pervagare orbem terrarium. inveni terras externas. cognosce miros peregrines. eviscera eos” ̴ “Join the legions, see the world, travel to foreign parts, meet interesting and exotic people, and disembowel them.”
Parliament's main field army's cavalry were equipped from donations and money from the London area and these records show attempts to focus on two pistols and a sword. However it has been put that a carbine (to use a phrase) could have been sustituted for at least one of the pistols for a period. What regional forces had depended on what they could obtain. I need to find my list of what Henrietta Maria brought from Holland to take this further.
Interestingly, the NMA cavalry in Ireland during the 1650's had to be given carbines to allow them to combat the Tories.