Well, I think we are mixing things in this thread. The OP wants an "anarchist victory" in the civil war, but we are mostly guessing about the conditions for a republican victory. To be honest I'm not sure if I have understood the OP question. An anarchist solo victory in the civil war is very very unlikely since they have to count with the other political sensibilities, in the republican side, or at least with most of them, to hop some success in the war. Perhaps, after a republican victory, we could imagine some kind of anarchist overtook over the other political groups involved in the republicann side during the war, tough I find it also difficult. If Franco managed to build a new state it was because he managed before to unify all the political sensibilities on the nationalist side under his command and figure not without tenssions and difficulties. A victorious republic would have a similar problem (they had the same problem during the war, in fact). None of the factions alone could manage to keep the order in the country without concessions to the others or a unifying figure. We can ficure also that a victorious republic would have an early will to include moderate sectors of the right in the system, but that is irrelevant to our pourpose here.
Another problem for the anarchists is that they had strong support in localized parts of the country, mainly Catalonia (and there, clearly more among the industrial workers than in the countryside) and rural Andalusia.In other pars of the country theywere less relevant or simply insignificant. Even a "free" anarchist Catalonia would be difficult. Catalonia was one of the main sources of Nationalist volunteers for a reason. The powerfull catalan bourgeoisie, as all the bourgeoisies in the world, didn't like revolutions as did the traditionalist roots in many parts of rural Catalonia. I know that catalan nationalism has managed to project a different image of the role of Catalonia in the war, but the catalan society was as divided as the rest of Spain. Also catalan nationalism, even its left-wing, probably would clash with the anarchists sooner or latter. Anarchism and Nationalism are not compatible, not to mention that many of the supporters of anarchism in Catalonia were charnegos, inmigrants from other parts of Spain. Durruti himself was from Leon.
As mentioned by othe posters, the extreme decentralization and the somewhat complicated process of decission-making would be one more difficulty. Perhaps after the war, specially if the POUM can grow enough to support them, they could make some arrangements with the Republic to develop their social experiments where they had popular support. Let's say that, after a republican victory, the stalinist threat is took as the main concern for the vistorious republic, and stalinist discredit is profited by the POUM to occupy the PCE's place and more, becoming the main marxist party. Maybe, they could also attract the more radical elements of the PSOE. The problem is that we need to change some of the events during war, because to the end of the conflict the Communists had inflicted a deep damage to the POUM.
And that's all I vcan think for the moment.