How do I disable the stock Gallery app?
You can use an alternative launcher like Launcher Pro / ADW / Go Launcher etc. All of these have options for hiding apps from the app drawer.

Unfortunately, the Gallery app will still appear in SHARE and SEND TO menus in various apps. No way around that. If you would rather certain folders remain invisible to the Gallery app, place a blank file named .nomedia in the folder to keep it from being displayed in the Gallery. Unsure if Quickpic will also have same functionality.