I have a few pages similar to this in my groov project.... You will get the hang of moving gadgets to the back as you are done with them and so any new ones you place will be on top.
The order you build also helps get things right the first time. Map on first, then each gadget with the navigation gadget last.
Lastly, you can just click and drag over the page, this will show the gadgets on the page and you can then start drilling in as needed by sending the ones you don't want to work with to the back.
Lastly, it might help if you lock the base (I am assuming the map image) layer. This way it wont move around as you work with the other layers.
Hmmm, this sounds like it would be a good topic for a groov Workshop image as seeing this being done might be better than talking about it....