To summarize your timeline, then:
turn 1: Does Turkey start at war, on only on it’s own turn? Do Belgium and Serbia start at war, or only if they’re attacked?
turn 2: Chemical weapons used for the first time (Allies will only use gas if CPS already have done so)
turn 3: Italy joins the Allies
turn 4: Bulgaria joins the CPs
turn 5: Portugal joins the Allies
turn 6: Romania joins the Allies, Arab revolt begins
turn 7: US Election; tanks used for the first time; Romania surrenders
turn 8: USA declares war (but doesn’t join the Allies)
turn 9: Greece joins the Allies
turn 10: Bolshevik revolution warps Russia into alternative universe
turn 11: Treaty of Brest-Litovsk seeds Western Russia to Germany
turn 12: Bulgaria surrenders
turn 13: Allies invade Russia, CPs collapse
turn 14: Russian civil war continues
turn 15: Russian civil war continues
END: count up the number of capitals captured to determine winner
This rather nicely gives an event or tech development each turn