Yes they were used to harass the enemy, however, the horse archers and lighter equipped horse were used for this more often than not, however the infantry were extremely important for sieges, even though the they had a lower status than the cavalry. They were armed with bow, crossbow or spear and shield. They did form up in a block formation armed with spear and shield front ranks and bow armed in the rear or separate firing over head.
There were elite units of horse as was the nafatin (fire-troops) on foot, were considered elite. Other foot for you to consider m'Lord are the naqqabun (miners/engineers), hajjarun (masons), najjarun (carpenters). These were most likely been paid salaries like other professional troops. Under Saladin, the army's support services showed how it outclassed the Frank's – Postal services for communications which included carrier pigeons and couriers, and fire beacons, cities would have arm bazaars, and key cities like Aleppo, Damascus, Cairo, and Mosul had weapons-manufacturing.
In terms of other units, Saladin utilised the best of the old Abbasid and the recent Fatamid systems buying pagan Turkish slaves from Asia (similar to the successful Ghulams under the Abbasids). However, Turks were the largest ethnic group within the army. Another important element are the Arabs resurgent in Syria, providing qufl – infantry raiders who specialised in harassing enemy communications and the lisus cavalry infiltrators disrupting enemy supplies.
Another harassing force was the mutatawi'ah a sort of religious volunteers who although were often around for only short periods, effective troops, however, tended to be on foot (not exclusively!).
Lastly two other units: you have the ahdath an urban militia generally used to police cities but could in an emergency fight alongside the regular army, and the rajjalah often despised by other local troops.
All this information and much more can be readily had via God's Warriors by Nicholson, H & Nicolle, D. as well as Warriors of God by Reston, J, Medieval Warfare Source Book Vol.2 by Nicolle, D, and plenty more but I'm in hurry today.
If you want detail from a wargaming perspective find this treasure chest: "A Wargamers' guide to the Crusades" by Heath, I. But expect to pay a fair bit as it is out of print and rare.