You can do several partial selections, save them to channels, and then create the final selection by combining (some of) them. See here.
You can move several channel together. Jut chain-link them, make them visible and select one of them, then in the Move tool use "Move active layer" (which in this case won't be a layer). The only catch is that channels are clipped to the canvas and during the move the preview only shows the one you are dragging (the others are moved only at the end).
You can move several channel together. Jut chain-link them, make them visible and select one of them, then in the Move tool use "Move active layer" (which in this case won't be a layer). The only catch is that channels are clipped to the canvas and during the move the preview only shows the one you are dragging (the others are moved only at the end).