1. Yes, but only on AI worlds.
2. Losing your ships on AI worlds is the only way Reprisal is generated.
3. No, and in fact, Cleanup Drones are a largely deprecated unit. AIs don't have Remains Rebuilders, and even if they did, nothing they currently have leaves 'remains'-proper except Mines.
4-5. There is no reversing Reprisal. Don't let the ships actually die(retreat your damaged ships back through the wormhole, repair them with Engineers, and come back later). Use cheaper(in Metal value) ships. Attack with overwhelming force, so the enemy doesn't have time to inflict losses.
Although, if you're seeing Reprisal Level 3 warnings, you are taking extremely excessive losses. There's probably a very nasty Guard Post, Fortress, or an Orbital Mass Driver that you need to take note of, and be sure not to operate ships in the vicinity that are weak against it.
Fortresses wreck anything in range that doesn't have a Polycrystal hull, for example. Orbital Mass Drivers target and generally one-shot any hostile Starships on the whole planet(and as Starships are very expensive, this is one of the fastest ways to rack up massive Reprisal levels).
Look around the enemy planet, mouseover everything, and note the descriptions and damage bonuses they have. You need to find out what specifically is killing you, and probably send a more specialized strike force to remove it before you can go back to 'business as usual'.