Hawaii, the BIG Island, for first timers
Depending on where you decide to stay, you may want to re-arrange these days to suit the distances and drive times. It is indeed a BIG island and the distances between areas is actually pretty significant. You'll likely want to stay near Waikoloa Beach, or Kailua-Kona. Waikoloa has the larger hotel chains and condos on golf courses. Kailua-Kona is more casual and has some great Airbnb deals close to the water.
Hot tip: rent a 4x4 or other vehicle with high clearance so you can access some of the more secret beaches on day 3.
Day 1: Arrival + Beaches
Get settled in to your hotel. If you're staying up in Waikoloa, take a walk through the Petroglyphs. If in Kona, take a neighborhood stroll to get your bearings.
For lunch, northern options include something at the Kings/Queen's Markets, Lava Lava Beach Club, if you're in Kailua/Kona, try Huggo's, Umeke's Fish Market, 808 Grindz or Pau Hana Poke.