If arriving at HNL airport, there are rental car shuttles immediately outside Baggage Claim. Depending on the Terminal, and if you had only light luggage, you might ask Airport Staff on walking to car rental on-airport sites.
Waikiki-area has a great selection of hotels. Hilton, Marriott, Hyatt, etc. Most have fine pools. My favorite, not too expensive, is the large Hilton Hawaiian Village (ocean front location).
Hotel information desk will provide large list of local "good eats".
Again, hotel information desk will provide tourist site information. On "Pearl Harbor Memorial" visit, there is only ONE approved boat access to step onto memorial (as compared to boating around it).
If you are a Costco member, they have many Hawaiian food items that are very reasonable.
In addition to credit cards, cash use should be similar to your personal experience in most cities you have travelled to. Hawaii is expensive, partly because most items need to be shipped in from elsewhere.
Now is a good time to book hotel and car.
By the way, do ask hotel tour desk about choices for a LUAU.
Reat assured...you should have a fine visit to "Paradise".