Great decision. Sorry, I can't help with condos, but a lot will depend on your budget and criteria. People here seem to like Sealodge (on a cliff overlooking the beach with beautiful views, in Princeville) and Hanalei Bay Colony (which looks sensational to me).

Sounds like a great plan! Let me know if you need any help with Waikiki hotels or activities. Sorry never been to Kauai.

Hanalei Bay Resort in Princeville is very nice, two pools and a paved path down to the beach (if you do not want to walk back up they have a phone and will send a golf cart for you). The Hanalei Colony Resort looks nice, about 10 minute drive from Hanalei with a nice onsite restaurant, but the beach there is not swimmable, too rough most of the year. It is in Haena.
Songdoc likes the Sealodge condos.

I would also recommend Hanalei Bay Resort. Go to summitpacific.com and check out what various owners have for rent!

I just looked on summit pacific and Sealodge D9 is available for your dates. Looks like a place I would definitely stay in.

When you land in Honolulu, there is a stand of several individually owned beautiful hand made fragrant leis. You need to drive there (it is within the airport area) I'd suggest you go there and choose several leis.

It is a wonderful first sight, smell and aloha of Hawaii.

September is a wonderful time to visit Hawaii. The busy summer season will have ended and you'll find hotels, restaurants, attractions and activities not at all crowded.

We'd really like to get a condo or something similar with a kitchen. Any recommendations?

vrbo.com

Katzgar, which island?

perfect choice on 2 days Oahu for first timers...hit the norths shore, over the pali (stop at the lookout!)to Kailua and a few of the visitor favorites(arizona memorial)...then outta there
Kauai in september is awesome! summer crowds have greatly diminished meaning all the choice little shoreline cottages are wide open, to be within walking distance of ocean and town. VRBO/Homeaway/airbnb all direct to what resonates with you. Plenty of deals in the offseason with fully stocked cliffside condos over looking the ocean and reefs where the trades cool all day... placed friends and family in alot of them. do good searching! Hanalei bay resort in princeville has nice time shares as stated above. (Big Isle is epic wide open adventure...can spend hours suggesting Hamakua coast, volcano cottages, etc..) ...back to the Garden island..
Kauai soothes. September is hottest time of year allowing for epic hikes, ocean savoring, quiet shoreline lingerings....IF IF decide on Hanalei, hit the haraguchi's hawaiian lunch wagon for plate lunch with daily kalua'd pork/homemade hanalei poi kulolo(taro and coconut milk). We grab fresh off the boat sesame ahi poke and crab rolls from the Dolphin's fish market and pack it up for a day at any number of secluded quiet beaches... the fun of Kauai is spontaneity = just flow. Get up early for Hanakapi'ai hike(first beach into Na Pali trail), snorkel the abundant reefs of Anini and Haena..journey to Waimea canyon and south side for a day..
almost as much fun to anticipate and plan a trip...plenty of great input from all on this sharing site! a hui ho... see you soon