What kind of troops made up the army? What special roles did certain units/squads hold? What weapons were common and what weapons were more specific to certain groups? What was the ethnic makeup of the army/ certain groups? Etc.
Also, where could I find more info on this topic?
I'll refer you to two excellent books on the Ottoman Empire in WW1 where you can find detailed information about your questions. I'll try to provide brief answers to some of your questions that I know about, though keep in mind that I'm not a military historian and should what I say contradict something in the recommended books, I must be the one who gets it wrong!
The troops that made up the Ottoman army were pretty much what you would find in the European armies of the time. Specifically, the German army, because from the beginning of the 20th century onwards, the Ottoman Empire followed the Prussian model closely in modernising its army. Young Ottoman officers were educated by German (Prussian and some Bavarian) officers who did leave their mark on the Ottoman army. Not to mention the fact that many German officers directly commanded Ottoman units in WW1, such as Kress von Kressenstein and Liman von Sanders. As for what special roles certain units and squads held, I'll have to refer you to the books.
As to be expected from a German ally, some of the more prominent weaponry the Ottomans possessed were German-made. A variety of rifles made by the German arms manufacturer Mauser was used by the Ottoman army, with the most modern one being the M1903 Mauser bolt-action rifle. But there were other rifles in use too, with the British Martini-Henry's (commonly known in the Ottoman/Turkish folk culture simply as Martini) too remaining in use. As for more sophisticated weaponry, particularly important was the Krupp artillery. These were among the pride of the German war industry. To the dismay of the Allies, the Krupp artillery would go on to play a key role in the Gallipoli campaign.
The ethnic composition of the Ottoman Army reflected the ethnic composition of the Ottoman Empire, to an extent. Turks generally served as the main reserve of troops, but Arabs, Kurds, as well as non-Muslim minorities provided the army with troops. When it comes to the officers, it was certainly much more common to find Turkish officers. Nearly all 'big name' Ottoman officers from WW1 were indeed Turkish: Enver Pasha, Mustafa Kemal Pasha, Esad Pasha, Cemal Pasha, Nureddin Pasha, etc... That said, there were a non-negligible number of Arab officers, a significant portion of who formed the backbone of the newly arising Arab armies from the impending defeat of the Ottoman Empire onwards. There were also non-Muslim officers, though very much limited in number in comparison with Arab and especially Turkish officers. Interestingly — interesting from a modern perspective with hindsight, at least — there were some Armenian officers too.
For more detailed information, you might want to check Edward J. Erickson's Ordered to Die: A History of the Ottoman Army in the First World War (Santa Barbara, CA: Greenwood, 2001). A more recent book that is similar in scope is Mesut Uyar's The Ottoman Army and the First World War (London and New York: Routledge, 2020).