Eric, that would be Mokelueai beach you visited off Farrington Hwy, which, as you said, is only accessible with a car, and during the day for safety purposes. Not recommended to walk out there.
Joseph, ok I understand, but you need to know that if you walk into most hotels in Hawaii you will pay the highest price for not the best room. Best to pick a time frame of maybe 1 week for Maui, 1-2 weeks on Oahu, as there is more to see here in my opinion. You will spend the romantic time on Maui, as it's easier to find more privacy there IMO.
The reason I mentioned some of the places I did was for you to get good deals, that's all. I can get on the plane in LAX wearing just what i have on, and my technical gear in a 2600cu pack. Once I get off in Honolulu I head over to the Ala Moana Center for a bite to eat, catch a bus down towards Pearl Harbor; getting off there allows me to walk across the street to the Aloha Staduim Flea Market and buy another pair of 'island style shorts & shirt' for cheap which double as souviners back home.
If you really love snorkeling and anticipate doing it more than a few times, which is possible, then strap that gear to your backpacks and carry them on the plane. If you ship them to a hotel make sure you send them DHL/FedEx, and alert the desk that your 'luggage' will arrive ahead of you, do not tell them the contents.
You are going to probably spend a night in a hotel in Hono', get up REALLY early and take your new bride over to DiamondHead and hike up to the top to watch the Sunrise. BRING JACKETS AND WEAR PANTS it's cold up there before Sunrise. Do NOT take the Hotel's towels up there, as they really frown on that....
After you hike down, grab your gear and go snorkel Hamanama Bay. I spent lots of time here, and since you own snorkel gear I can forsee you and the wife spending a Whole day here! Enjoy, bring a picnic lunch, but do not bring ANYTHING you cannot afford to have stolen. Since this is a tourist area there are druggies who patrol the beach watching for folks heading for the water. They ususally just look like someone sitting on the beach, usually alone, and they watch you setup your stuff, and head to the water. They watch you in the water awhile until they think you have relaxed and stopped watching your stuff....that's when they walk over to your stuff, drop a beach towel over it, and scoop up everything and walk away. Who's going to question someone picking up their beach towel? Smooth huh? Oh, gonna' hide those rental cars in the sand near your stuff, way old school here..the theives are VERY practiced. If you are'nt taking it into the water leave it in the rental cars trunk, which, even there can be screwdrivered in less than a minute. Valubles belong in a safe at the front desk of your hotel in Hawaii, sadly, the same as everywhere else these days.
Up on the North Shore you will enjoy snorkelling the Tide pools in Pupekea, near the fire stn/ behind the basketball courts. Be alert to the state of the tide, especially if you decide to catwalk the outer reef. Afterwards there's a Foodland across the street to buy a picnic lunch to bring back to the same beach. Whale watching from here is great early in the morning Sunrise til about 1000hr, again after 1500hr.
Up the road towards Haliewa past the fire stn, traffic light, parking lot on right, there's public bathrooms, behind which are some rocks with surf breaking on them. be careful here, I watched a guy get sweep off literally to his death one day. he ended up down the road at Waimea Bay the next day in the rocks; and perversely I was walking down the road and looked down and saw him in the rocks below. I called H 5'0 to come get him, not pretty.
Waimea Bay Beach is for sitting not swimming wicked rips here, yes, there are lifeguards here and people who don't respect the place are in the water. Keep going to Lani's to get back in the water fro more snorkeling.
Up the road toward Haleiwa along the Kam' Hwy the Bus, if you are on it, can drop you at LANI'S, the beach where I can almost 90% guaruntee you will find sea turtles to snorkel with near a shore side reef. Be careful of the swell and state of the tide in this area, it can be rough, as all water in Hawaii can. If driving park on the left, farmside of the road, and be careful crossing the road here.
Up the road in Haleiwa town there is a beach on your left after you turn left up the road towards town. Park near the War Memorial, no methheads here as opposed to the first parking area you see. At the Memorial you'll see the local club canoes, and it's easier to snorkel here. No dive knife needed for snorkeling, so you should be able to carry it all on the plane.
Over the Rainbow Bridge you get into town, can walk it if you are using the Bus, fro the beach here. Lots of cool stuff and nice folks, my hometown on Oahu.
As far as slcklining on the beach, no. If you put it up and some locals that are'nt friendly take a liking to playing on it, you might find your wife wanting to move on, yet you can't w/o starting a hassle. Stick to what I'm advising and you should have a nice long marriage after this trip.