No resources are recovered when scrapping a ship/orbital. They may add that ability in an upcoming update.

No way to give up planets yet (this will be added in the next update). Unfortunately, you're stuck where you are. You'll just need to research bigger harvesters and start bringing in resources from other sectors. Either by building outpost ships or by capturing other player's outposts. Obviously colonies are only created by making colony ships or by taking them from other players. You'll need about 15 cruisers to take a new colony under 10-12Mu.