I would be most interested in hearing how a syndicalist revolution planned to defend itself against counterrevolution from both internal and external sources.

Oh, it can't. No socialist system can without turning to evil, which is a big problem with the theory.

"Yay, we're all brothers and sisters now. Oh, wait, Germany is invading us. Here, have our brothers and sisters in Ukraine to leave us alone, Germany. Oh great, now we're being attacked by other nations and the former ruling class. Shit, that's causing disruptions in the food production and supply. Well, our brothers and sisters doing the heroic fighting need the food, so sorry, starving brothers and sisters, tough decisions need to be made. Stop eating your children, it sends a bad message about communism. Wait, now the trade unions in the soviets are complaining about these tough decisions we have to make? Fuck you, trade union brothers and sisters, you're out of the soviets. Yeah, well we don't give a fuck if you are the only legitimate proletariat in the dictatorship of the proletariat, we have to defend the revolution. Hey, over there, what do the heroic sailors that sparked the revolution want? More democracy? A say in where food is allocated? Fuck you, heroic sailors of the revolution. Shoot them. These grumblers over here as well please. And those commanders of the people's army, they look like they're getting ideas. You know, a powerful secret police sounds like a great idea."

The advantage that syndicalism might have, in the current circumstances, is that it's highly democratic, and it's a slow growth of socialism from the bottom up. As you point out, it doesn't do well defending itself from enemies (or even supposed allies, as the CNT found out in 1936), but when the global economic system is falling apart, that's less of an issue. And if/when the economy and/or civilization starts devolving, self-organizing communities are going to wield a lot of social and economic power.

Just my own personal opinion, of course, things might work out differently.

I think that since the majority of revolutions that will kick off the global conversion to socialism will be heavily based in the peasantry

Well, the thing is that we don't have a say how societies with peasantry organize themselves. We in the former imperialist nations have a nasty habit of thinking so, but that's our culture for you. We do have a say in our own communities, and a better shot there at introducing the better elements of socialism and avoiding the pitfalls.