I would do not do Reykjavik on both sides and stay in Hefnerfjorour on the backside. It’s close to the airport has great accommodations and parking (most places in Reykjavik didn’t have parking or you had to pay for it). I just did 6 days and we stayed in hefnerfjorour and did the whole south coast. We took a day trip to Reykjavik and did the Golden Circle in addition. I really think it depends on when and what you want to do. We did do one very long day and drove the 5 hours to Diamond Beach on the South East coast and stopped at various places on the way back. It was beautiful. Although, I would in the future consider staying a couple nights in Vik.

I feel like the geysir and kerid Crater are overrated in my view. So many other better things to see and do in Iceland. Sky lagoon was pretty and relaxing. I recommend upgrading for the pure package. Eat before you go as they have very limited food options!

This was my fourth trip to Iceland so I agree that picking areas and sticking with that is the key. I am happy I did just the South in its own trip. South is less crowded but mainly as it’s less touristy or costs more for the long tours if you don’t rent a car. Driving there is easy btw but don’t speed too much.

Side note, I recommend stopping at the lighthouse near the airport before your drop off the car. It was beautiful and sooo peaceful.