The penalty for rape would be determined by the parties or if there is no agreement the fine would be determined by the court.
In the Icelandic system if someone was charged with murder they were outlawed. Anyone killing an outlaw was not prosecuted. Housing or aiding an outlaw could result in prosecution (fine to the family or being made an outlaw as well).
Killing was different from murder. If the death was not murder (manslaughter), a fine is paid.
The murder rate for those 300 years in Iceland was much lower than current US murder rates.
The compensation method as opposed to our method is more economically efficient. A fine is a costless punishment; the cost to the payer is balanced by a benefit to the recipient. It is in this respect superior to punishments such as execution, which imposes cost but no corresponding benefit, or imprisonment, which imposes costs on both the criminal and the victim (through taxes).
The downfall of the Icelandic system was when the Catholic church came in, essentially disrupting the power balance that had evolved over centuries. They were able to use their economic imbalance to usurp the political structure much in the same way that large nations subsidize their own political system on smaller nations (ie Russia funding Cuba’s communism, the US funding western systems around the world, etc.).
On a seastead I would take the victim compensation a step further than what they had in the past. A victim who was poor would have a hard time paying to prosecute the offender. So they would essentially sell their case to someone who did have the means to see the case all the way through to the end. The owner of the case would then be paid the fine. I think this is a good opportunity for blockchain technology. Create a new blockchain token that represents the case, people can buy and sell based on whether they think the case will be won or not and what the compensation will be. The victim can sell their tokens to pay for prosecution as they see fit.