To respond to your points:
To be fair, I prefer stacking Galacia over hitting Poland AH1. I only brought up the possibility of hitting Poland as a hypothetical.
I don’t particularly care about winning in Serbia round 1. I only even attack Serbia at all because the rules of the game force you to. The rules of 1914 allow you to choose whether or not to press combat each turn, so you can simply have the Austrians not attack the Serbians each turn, which allows you to potentially roll 3s with your stack there instead of 2s (assuming the Entente presses combat).
That being said, I think I was a bit off in assuming the Serbia guys would be capable of hitting Romania round 2. You’d probably need to split the Galacia mega-stack to hit both Romania and Ukraine, depending on what Russia does.
You can most definitely contest Romania and Ukraine AH2 if you’re committing 100% of Germany’s buys towards Russia. Yes the battles won’t go in your favor initially (and you may have to spend some turns not pressing combat in Ukraine), but your objective in a Kill-Russia-First style of strategy should be to hit Russia on multiple fronts and force them to lose more troops each turn than they can feasibly replace. Starting fights in Poland (with Germany), Ukraine and Romania should be enough to accomplish this goal.
Side-Note: Your 10 INF/4 ART swings for 36 (8@3 + 6@2) and has a 60% chance to wipe the Romania stack in one round of combat. Those are pretty good odds, but it’s not exactly consistent, especially considering that a big chunk of your strategy hinges on having the Romania stack available to march on into Ukraine AH2.
On the topic of fighting/holding off Italy, I prefer killing Italy first as Austria over killing Russia first, but that’s beyond the scope of this conversation. However, because Italy goes after Austria, you can send some of your turn 1 buy into Trieste Round 2 to slow down Italy if you’d rather send 100% of the Vienna guys East.
I don’t have much more to add, really. If I were Russia playing against this I would just shuffle all of my units into Ukraine R1 and hope that France/Italy/UK can do something productive in other theaters.