There are a total of 38 Shopping Terminals. You will run into most of the terminals when following the path of the story. They are really easy to see since they are relatively big and red colored. However, some of them are very easy to miss when you are busy with fighting enemies (especially the terminals during boss fights). The good news is, that the ones you already found will be handed over to all your future playthroughs. The bad news is, that there is no way to see how many you found already. Once you find and enter a terminal you do not have to buy anything. The game will save your progress immediately after you entered the terminal. You can also do this via chapter select (unlocked after beating the story) to go back and open the remaining terminals. You can quit to the main menu right after opening the terminal, your progress will be saved.