A lot would depend on the exact date of the POD, and how much latitude you gave me. If early enough, i don't give the Austrians a blank check and i don't go on vacation in the late summer. I also start co-ordination between the Germans and A-H staff. If i did give the blank check, i have A-H accept the Serbian reply. Yes, Russia is getting stronger, but Germany will also get stronger, and France has a low birth rate and the 3-year-conscription drags on the economy. A-H needs to reorganize, and I know a lot of things to improve the German military, but you seem to want a war.
Britain was likely to enter the war anyway, just not necessarily immediately. It is a hotly debated point, but i believe Britain would have intervened. It is also difficult to overhaul a mobilization schedule at the last minute, and the a lot of French industry was captured. So I would still execute the attack in the West, but put more focus on sweeping the channel ports. The objective is to take a much of France as possible, to weaken France. I would also halt the counter attack in the A-L before the heavy forts were attacked.
The real problem is in the East in Lemburg and Pemburg, and the low quality A-H army. The CP need not to lose so these two towns for both the troops for later on, and to make less likely Italy enters the war. Or, hopefully at least delay Italy entering the war. As soon as the push into France hits heavy resistance, and the Germans stop advancing, I will transfer troops to help A-H as fast as possible. Even saving one of the cities will help a lot. As reserve corp become available, they will mostly be sent to the east. If i have control/influence over A-H, the second army goes straight to Russia, and i begin a full mobilization as soon as the Serb reply is received. I will basically use War Plan Russia, not War Plan Balkans. Also no unrestricted warfare, I want to give the British blockade some time to have more effect on the USA and I want to have enough ships to be decisive when applied. Diplomatically, i will push for Romania and Italy to join the CP. Short of A-H territory, I will give them the world to join the CP.
The 1915 strategy will be what you suggest, east focus, strategic defense in the west. Order of Priority of task, done til completed.
1) Don't lose land on any front.
2) Save Lemburg, Pemburg.
3) Conquer Poland to shorten lines, kill Russians, and hurt Russian morale.
4) Knock out Serbia.
5) Knock out Romania if in war against us.
6) Take land from Russia to drive Russia out of the war and gain resources.
7) Knock out Italy.
8) Knock out France.
BTW, the Germans did try to envelope at various places, but they the Entente could generally pull out forces before surrounded. In WW1, the attacker walked, the defender used trains.