Osaka is easy. The Osaka Metro covers everything and your Centara Grand hotel is right next to Namba Station — the biggest hub in south Osaka. Most of the places you’re hitting (Dotonbori, Shinsekai, Shinsaibashi, Amerikamura) are walkable from the hotel. You’ll use the metro less here than anywhere else.
Pro tip: Osaka is the most walkable city of the three for your itinerary. Dotonbori, Shinsaibashi, Amerikamura, and Namba are all within a 10-15 min walk of each other and your hotel. Save the metro for Osaka Castle, Shinsekai, and the airport.