For physics, Bullet is the best choice. However, consider whether you really need a physics engine, or whether a simple collision system (like Panda’s) will do. Many kinds of RPG games will not benefit from a full-blown physics engine, and this will incur a significant extra amount of effort and time to implement.
You could embed the browser plug-in in an HTML view, but I’m not really sure if it’s the best solution. A better way to embed Panda into another program is by getting the underlying system-specific window-handle (HWND on Windows) from the program, and then telling Panda3D to parent its window to this handle. This has been done successfully to embed a Panda3D window inside a window created by another toolkit.