You may want to expand your search. North Myrtle Beach isn't romantic, Myrtle Beach is spread out, mostly chain food and jammed in July, Charleston's interesting with the best 'scenery' outside the city visiting the nearby plantations, King Street's OK but other than Ben Silver's (if she wants to buy you a $150 tie) I've never thought the stores were that interesting.
The City Market is much more flea market than treasure trove - Charleston does have many fine restaurants, but no 'beaches'. Isle of Palms is surrounded by stone rip-wrap, its eroding; Sullivan's Island is essentially residential but there is a street of bars a few blocks back from the surf ... though very little shopping. the 'nearest' actually accessible 'beach' (from downtown) is Folly Beach - which they claim is 10 minutes from downtown, when in fact it's more like 30 and a pain if Folly Road is jammed, which in July is normal.
Seabrook has no shopping to speak of, Kiawah is a residential/golf resort, Hilton Head is also spread out, its 'beaches' paltry, narrow and parking non-existent unless you're staying on the oceanfront.
Fripp Island's nice but isolated, no shops - a neat 'grocery', though - and at one time a Polo outlet store, although I'm not sure it they have it any more.
From Kansas City you might enjoy Savannah much more, Tybee Island boasts an excellent beach far more convenient to downtown than any of Charleston's surrounding island beaches. Also St. Simons Island, which when reading your 'wish list' comes closest IMHO to matching all your wants - quaint shops on Mallory Street in the 'village' - a neat lighthouse, lots of great restaurants (NOT 'chains') and several very nice hotels or oceanfront condominiums to choose from. A 'cross the inlet' trip to Jekyll Island is a must - its membership in 1900 controlled 25% of the entire world's wealth.
Another consideration (from Kansas City) if 'East Coast' is what you want should include Amelia Island (the town of Fernandina Beach) - 'Centre Street' has wonderful shops, the restaurants and bars are special (including the oldest bar in Florida) ... west coast you should look at Destin, the finest beach I've ever visited, its sand white as salt, the water so clear you can wade out chest deep and still see your feet.
St. Augustine is a wonderful city to visit, great shops, the fort, terrific nearby beaches on A1A - fun 'old fashion' things to do, and you'll be walking on the oldest streets in America settled by Europeans - there's almost always a breeze, even in July.
Best bet? Fly into Myrtle Beach, rent a car (that you can take 'out of state') spend night 1 in Murrells Inlet at the Inlet Sports Lodge, visit the Marshwalk for dinner, check out and visit Brookgreen Gardens on your way to Charleston, try the Mills House on Meeting Street or the Indigo Inn Night 2 - eat at 82 Queen, pick any plantation, Boone Hall in Mt. Pleasant or anything out Hwy 61 - then take 17 South to Hilton Head, stay at the Westin on the ocean night 3 - eat at the oceanfront seafood luau adjacent to the hotel on the ocean -then travel to Savannah, have a late lunch upon arrival at Mrs. Wilkes boarding house, check-in the Marriott along the River Walk night 4, great shops and bars and scenery. Drive to St. Simons Island, check into the King & Prince for night 5 - visit Mallory Street then Jekyll Island on the way to Amelia Island - check into the Ritz Carlton for night 6 - explore Centre Street, then on to St. Augustine for night 7 - see the fort, the Fountain of Youth and stroll through the oldest gates in America along the quaint shop row on a street laid out for carts not cars 400 years ago.
Return your car to the airport in Jacksonville, several direct flights to Kansas City.
