Gently mix crab, 1/2 cup panko, mayonnaise, eggs, red pepper, green onions, Dijon, Old Bay, black pepper, and cayenne in large bowl, preserving crab lumps.
Form about 32 balls, 1½ inches across. Put remaining 1/2 cup panko in shallow dish; lightly coat balls.
Heat large skillet over medium-high; sear balls in batches 1-2 minutes per side until lightly golden, not fully cooked.
Line slow cooker with parchment; arrange balls and drizzle with melted butter.
Cover; cook on low 2 to 3 hours until centers 160°F (71°C). Only then switch to warm; serve with toothpicks, lemon wedges, and remoulade.