You can get the coordinates by:
panelOne.x and panelOne.y
panelOne is the id of your panel. e.g. <mx:Panel id="panelOne" ...>...</Panel>
To add a new panel right next to it you have to set the x and y for the new panel like this:
Hope this helps.
If this is something you're going to be doing a lot of, you might want to just stick the panel in an HBox and use hbox.addChild() to add the next panel. Plus if you get in the situation where you've added 3 panels and you need to remove the second one, this way will save you from having to move everything around yourself.
if you want to add the panels ina flow layout there is a flowContainer component available .. google it.. it will automatically places the components into the next line if it is too much for the current line.