Looking good, only thing to consider now would be to take advantage of the way Ext passes objects to constructors so instead of a fixed list of parameters this could become something like;

```
_buildTermStore: function (storeConfig) {
    return new Portal.data.TopTermStore(storeConfig);
}
```

This allows future parameters to be added seamlessly, it also means that the `_buildTermStore` method can be removed.