Ah, so you're trying to give the Soviets an opportunity to take advantage of the revolutionary wave, then? Baltics, Finland, Hungary, Poland, Germany and beyond? I've tried to pull that off for years.

It's a way difficult project, man. I've come to the conclusion that the reason the Soviet Union didn't work was because the Russian Civil War lasted so long and was so horrible that it militarized politics, culture, economy, society, a mark that lasts to this day. The reason the RCW was that bad was because the Bolsheviks, really only held the allegiance of twenty to thirty percent of the population, and they wanted to take power completely. Any time a minority group like that tries to take control of the majority, especially a vast land empire like Russia, it's going to get bloody. The Bolsheviks, by advocating a one-party state from the get-go, doomed themselves to failure.
That's the natural logic of the situation in the Soviet Union. What you are trying to do is cheat that logic, which has happened with others things in history, but you're going to need to do a lot of it, if you want to create a more successful USSR. Lots of lucky breaks.
The Czechoslovak Legion butterfly you've suggested... it could happen, but not really because Leon Trotsky is not being pressured by the Germans, but because the Chelyabinsk Soviet, which was largely self-governing, did not order their disarmament after they arrested some of the soldiers for fighting with Austro-Hungarian POWs going to the front themselves. That's a major butterfly and a lucky break for the Bolsheviks. The Legions, you see, had a very tough time getting to Vladivostok, not just because of Trotsky, and so avoiding all those problems is possible, but not too probable.
The Allied governments, however, didn't just intervene to rescue the Czechoslovak Legion, not by a long shot. That was just a useful PR move. You're still going to have landings in Archangelsk and Murmansk, Siberia and so forth. And those Legions that are still waiting for a ride to Europe by August 1918 are going to be instead enlisted by Allied governments to help take the Far East. Maybe only a quarter of them left by that point, maybe less, but still substantial. The Legion wanted to do whatever the Allies told them.
So, you've given the Bolsheviks a little more breathing room, including Ukraine, that's a big deal. You can butterfly away the worst of the Czechoslovak Legions, that'll help. But you're still going to have every Allied government from the Japanese to the Greeks trying to take out the nascent Red forces. You're still going to have to worry about the Tambov Rebellion, Ukrainian seperatism, famine, and Polish expansionism. With more German forces during the Spring Offensive, you've bought yourself about a month, as it'll take longer to take down Germany... there's a lot of problems to face.
Overall, things will definitely be better for the Soviets and the Red Army... but it won't be as rosy as you describe. No fighting outside of the peripheries? Ah, if only it was that simple and the Bolsheviks could extend their influence that quickly

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Peter said:
It seems very optimistic to expect peace with no concessions.
Yeah, they were very optimistic. The Bolshevik foreign policy was... incredibly idealistic. They believed they were breaking new ground, that this was a time of destiny when fantastic things would occur, because socialism had never been really tried before and it would result in all kinds of wonders. Very little understanding of realpolitik at this point.