If you're referring to renting out your home on services such as Airbnb, I would recommend looking at what are called Homeshare policies. A few companies that provide them (in addition to the companies you mentioned) are Slice, Progressive, and Allstate.
Unfortunately once the insurance company has been notified of a crash the information will be documented on the CLUE report of the driver involved in the accident. Since there is no way to say with any certainty how the incident will impact your rate, as that decision is ultimately up to Geico, proceeding with the claim or dropping it will not change the end result concerning your rate.
It really will depend on how your previous accident was categorized. If you were considered to be at fault in the previous crash then your accident forgiveness was likely used during that particular claim.
It really will depend on whether your friend's auto insurance policy includes comprehensive coverage. Beyond that, the damage to the paint will have to be higher than his deductible before his insurance company will pay for anything.
In New Mexico, our State of Insurance report shows that an at fault accident increases rates by an average of $596 additionally per year. Since accidents impact your rate for at least 3 years, you would be paying an extra $1,788 in premium over that time frame.
The resulting damage from hitting a pothole is actually considered an "At Fault" accident and would be covered under the collision portion of your policy. The reason this is the case is because insurance companies expect drivers to operate their vehicles safely and watch for hazards in the road to avoid frivolous claims.