PARKING: The fee is supposedly 20k, but no one asked me for it. You might get lucky too. Either way, it's worth it.
SNORKELING GUIDE: You will be approached by people offering to be your guide. Just say "no." If they persist, tell them you already have a diving course.
DIVING GUIDE: There's no need to pre-book as there are plenty available here. But since you're reading this, you probably like to be prepared. It's best to find a reputable instructor on Google Maps.
ENTERING THE WATER ON YOUR OWN: You don't need a guide. Guides may tell you that you can't snorkel alone, but you absolutely can. If you're a decent swimmer, nothing is stopping you.
LOCATION OF THE SHIP: The ship is 120 meters long and 25-50 meters from the shoreline, aligned with it. You can't miss it. The pin on Google Maps is accurate. Just explore and have fun.
TIDE: It's easier to enter the water at high tide due to the rocks, but any tide should be fine. I was there at high tide, which was good. Download the free app Nautide for the information you need.
TIME OF THE DAY: If you want the ship to yourself, go before 9 AM. Otherwise, any time is fine. I enjoyed the presence of other divers and snorkelers for orientation.
FINS: Yes, fins are highly recommended. The current can be strong, and the rocks can be annoying, though not sharp. You should be able to rent fins there.
SHOPS: The warung there has higher prices. A Coke is 20k. Still affordable, but more expensive than other warungs.