What would be the best accessories for pulling sumo?
Don’t know if I’m typical, but my personal experience is that front squats help my sumo dead very well. The relationship is linear; if my front squat max increases, my dead increases by a similar amount.
The conventional deadlift generally builds the sumo better than anything. Almost all of the great sumo pullers either use conventional as assistance in training or straight up build their deadlift strength with conventional and then pull sumo in meets (like Ed Coan).