In all likelihood he'd rightly see Germany and Spain as the weakest regimes in Europe, and take a very active role in fermenting revolution in those countries. Which given how he's also probably the Communist leader most aware of the political necessities of planning a revolution alive, he probably will succeed in. Not least because the Soviet Union under him, even if it's not rich, will certainly be a more open society which holds a better looking alternative system than OTL.
Trotsky was not an idiot, which is something I will stress all the time in talking about him. He knew what the military realities of Europe were and knew the Soviets could not win in a straight up war against everyone. Permanent revolution in Trotsky's policy means a use of the Commintern not just as a means to prop up Soviet Foreign policy, but as a means of exporting revolutionary practices, experience, and other generalized support for revolution as a primary purpose of Soviet Foreign policy, under the understanding that it was impossible for them to build a sustainable Socialism in One Country. Once that happens though everything is changed, because it essentially alters the equation.
I was more referring to Trotsky blatantly fomenting revolution in European countries rather than Stalin's Socialism in One Country approach. If in OTL a lot of European countries trusted Hitler more than Stalin until the Sudetenland Crisis than how would they react when the USSR would be more active in the whole "Global Revolution" in the interwar period than they were in OTL? Obviously, they wouldn't invade immediately, but if Trotsky doesn't industrialize as much as Stalin does and the West takes full advantage of the dissent in the USSR like Hitler didn't in OTL, it may be possible to topple the regime. Sure, the capitalist powers didn't defeat the Reds while fighting alongside with the Whites in the Russian Civil War, but they were also drained of manpower and trying to balance dissent in their own countries. If Trotsky tries to start a revolution in say, Germany, said powers might start having nightmares of at least a USSR stretching from the Bering to Gibraltar. And that could ratchet up the paranoia of "We're next if we don't do something" to the point where military action might be considered a possibility. All that being said, I'm sure I'm simplifying Trotsky's ideology so feel free to correct me where I'm wrong.
Just my two cents.