The best thing about this place is the LOCATION. Away from the hustle-bustle of the Kona side, yet near enough to Pahoa for food and supplies. Pahoa is a little funky town that we love, and the "new" Malama market is great.
There are some beautiful beaches close by, of course the black sand beach across the road, but McKenzie SRA is a must-see. Isaac Hale beach park used to be a premier surfer beach, but of course now it's fresh lava, but you're able to walk around and go to the hot ponds recently created. Go north on 137, it's a beautiful drive. There are some wonderful beach parks in Hilo, if you want to brave the traffic, go at non rush hour times. Any map will get you there.
We put over 1K miles on the rental car, but it was totally worth it. Volcano NP was totally clouded in, so we didn't go this time. The south end of the island has some gorgeous beaches, too, if you're brave, hire a local to drive you down to the Green Sands beach on the southern-most point.
They don't allow cars or pedestrians on the road down the Waipio (spelling) valley on the north side any more, but it's totally worth it to see from the point. It's magical. Stop off at Laupahoahoe park on the way, it's a must-see also.
Uncle Robert's is just a short drive south. Wednesday nights are the best times for Hawaiian music and dancing. There is a market there on Saturdays, and the walking path down the lava to the edge of the ocean is wonderful.
There were a couple of issues with the cottage, but the owners have been informed. Communication was great with them, and hopefully the issues will be resolved.
The end of March/beginning of April is still the rainy season, but we're from Oregon, so used to the rain and fog. If you don't like crowds and the touristy vibe, the east side of the Big Island is for you. The Kona side isn't that far of a drive, and if you want to experience a very different side of the island, both in climate and terrain, it's worth it. Waimea inland has a great pub, the Waimea Brewhaus. Good beer, good atmosphere and a friendly bartender when we were there.
So many recommendations. Another thing--when you arrive, don't look for a pink mailbox because it's not there anymore. Pay attention to the house numbers and you won't have trouble.