I do something similar as you suggest Durango with pikemen and arqs, usually it involves 2-4 arqs in line with 3-4 in a pike-gap line. I tend to leave the arqs in front to release volleys at incoming enemies (or appraoch swiftly the whole formation to the enemy and quickly volley) while ardering the pikes to take place at the front when the enemy appraoches. Sometimes this can be made locally ie a single pike can move forth of an arq in order to deal with a cavalry charge say - sometimes the whole of the pike line needs odering forth as the enemy has moved his own pike line. This is where the gaps between the pikes comes in; the make shooting by the arqs behind more effective as it lands on the rear/flank of enemy engaged units. However the same maneuver can be made with a solid pike line. Even in that case its worth leaving the arqs shooting, as if they make a single kill in an enemy unit they effect morale penalties.

If the pikes are reliable, like say swiss and swiss arm. pikes in vanilla its a solid combination, especially when coupled with light charger cavalry (hobilars, mounted seargets) and mounted crossbows. The light cavalry can harass, charge, mop, accompany to the exit etc. operating around the solid arq/pike base.