Very nice, thanks for sharing!
Yes, placing multiple markers to guide the drone towards the central landing pad is a great idea. You may also want to check out the ObjectDetect module, though we have not yet used it with a calibrated camera, but the location of the detected object in the camera view could already provide basic north, east, south, west guidance. You could grab several pictures of your landing site at different altitudes during an initial vertical takeoff, and then use those for the subsequent approach and landing, with no markers required at all if your envidonment has some distinctive features. Basically, save one image at 5m, then another at 10m, another an 15m, etc while taking off straight up from the target landing site. Then, during approach, the best match will be returned. Its location within the field of view and also which one it is (5m, 10m, 15m, etc) and how big it appears could help you guide the approach.
We just published a tutorial about the ObjectDetect module here: