Athens for 8 nights?

What many recommend is flying to the island on arrival day, then make your way back (flight or ferry, up to you) to put all of your Athens time together.
I can see a person loving cities and wanting to spend a week in Athens, but you do have plenty of time to add another place. It just depends on what you want to see/do!
Nafplio is a beautiful city and a relatively short distance from Athens. There are many great sites nearby. It is much easier with a car.

Athens is a wonderful city and there's more to it than just the tourist sites.

I would recommend spending 3 nights in Athens and 5 on one island.

Why Santorini? It's the most heavily touristed and expensive of the Greece Islands. Mid-April will be quieter but still will get crowds.

A closer and more laid back island would be Aegina just a short ferry ride away. It has most of everything one would want in a Greek Island including one of the best preserved Temples, beaches, abandoned Byzantine Village in the hills (The Mystras of the Aegean), seaside villages and is the Pistachio Capital of Greece.

It should be a lot more relaxing and less crowded than Santorini and far less expensive.

Another nice island a bit further away is Poros with a long and lively waterfront but the best part is uphill away from the crowds where you'll see beautiful white washed houses, narrow lanes, views and a real nice Greek Vibe.

If you decide on Athens day trips tend to be lengthy especially Delphi where most of the time will be on a bus unless you rent a car.

You could day trips to the one or more of the Saronic Islands which are the closest to the mainland like Aegina, Poros, or Hydra.

Leave in the morning, spend several hours on the island and return late day and still have more than enough time for a night out in Athens.

Still, I would spend 3 nights in Athens and the rest on one island.

I agree 100% with Tommy and Valadelphia, but it's mostly up to you to know what interests you.

There are enough things to see and do in Athens to spend 7 days there, or even more, but do you really want to? Maybe Athens won't appeal to you.

Do you want to spend time on an island? Go for it! Whether for a day or to spend 2 or 3 nights there

Going to Aegina is not even an hour's ferry ride. Don't worry, you're no more likely to get seasick on the ferry than you are to be sick on your flight to Greece.

Thanks all for the advice. I guess I honed in on Santorini because of the beautiful photos of the blue roofs and white washed buildings. I will look into Aegina!

Blue domes, white washed houses and windmills, you will see them on all the Cycladic islands, no need to go to Santorini if ​​that's the only reason you want to go there.