A few ideas for your consideration:
The CT is popular, but you can get away from the crowds by taking trails other than #2, the Sentiero Azzuro. Not many people venture to the higher paths, although we go in Oct so maybe it's nuts even on the high trails in summer.
The Amalfi Coast is rich with hiking from the famous Sentiero degli Dei to dozens of paths all over the Sorrentine peninsula. You can hike from cliff to coast, along cliff tops, etc.
Liguria, the region where the Cinque Terre is located, has more than juts the CT. Check out A Path to Lunch for many Ligurian hiking ideas.
The Maremma of Tuscany is coastal and offers hiking. Isola del Giglio is delightful for a day or two of hiking with views of water. We just went there a few weeks ago, but I understand August is a nightmare with all the people who hit the beach then....
The Lakes aren't exactly "coastal" but along Lago di Como is the Sentiero del Viandante, 45km if you want to dot he whole thing.
Edit: BTW, Oregonian here. We've been in Italy 2+ years now!