Advice for a few days on the Tuscan Coast

We stopped for a few hours in Lerici while waiting for the ferry to Portovenere. It was at the end of Sept. and as a resort town everything was pretty quiet as the season was over. Interesting town, nice seafront. Ferry will take you to Portovenere just outside the CT region. I also liked Liverno just north of the CT. Great beach, station handy for getting to Pisa/Lucca. Both Liverno and Lerici are resort towns so may not be fully open in April.

Lerici in southern Liguria was the first place I ever visited in Italy, and it's still one of my favorite places. We visited as a young couple who like to walk a lot (even if it means walking up a mountain after dinner), but it would be easier with a car. Bus service is limited, but you can always pay for taxis when needed. We were picked up at Sarzana train station by our host, and we caught rides to Tellaro and Montemarcello for hiking. Ferries should be running. April will be quiet and too cold for any beaches, but the hiking should be excellent.
The northern part of the Tuscan coast is flat and sandy, has better train connections. Viareggio and Livorno, although not quiet villages, would be my choice in this area in April.
Further south in Tuscany, the coast again gets dramatic--you have Ucellina/Maremma park, and there are many small towns along the coast or just inland that make for a nice stay. We visited this area with a car, so I don't know how easy it would be without.
Last, a bit further south you have my most favorite area of the coast, the Orbetello lagoon and Monte Argentario peninsula. If you were flying out of Rome, I would not hesitate to recommend it strongly, but I think you should probably stick to something closer to Pisa given the public transport.
Portovenere probably has the ideal combo of bus connections via La Spezia and proximity to the gorgeous Bay of Poets, so that is probably your best bet.

Santa Margherita is a great seaside town to spend 2-3 days. Outstanding restaurants and cafes. The beaches are real nice as is the harbor. Stay at Hotel Continental for a real splurge. Check out their “pool”, which is actually the sea. Wow

Will traditional seaside resort towns be open in April? Not sure it is warm enough to swim as i mediate post above recommends. I remember heading out to 'the beaches' near Newport RI one april looking for a clams and chip shack... not a soul for miles. Did find a great Portuguese seafood restaurant and deli inland though.
Though I digress. Perhaps define coastal expectations?...though CT congers up a pretty good image.

If you’re thinking of hanging out in a beach town, this won’t exactly apply. Although if you want to be near the coast, there’s an 18th Century Tuscan home near Castagneto Carducci, about 80 miles southwest of Florence, and less than 4 miles inland from the coast. They have 2 apartments there, which include their own kitchens and sleep up to 5. Chicca also does wine and food tours, classes, and during the Pandemic had held Zoom cooking classes that have a following of over a hundred people from around the world. She and her husband do their walk each evening to the coast and back.

If you eschew any itinerary, you could still spend the time in their quarter-acre garden, playing bocce, and enjoying the countryside just inland from the coast, or in the hilltop town Castagneto Carducci (pop. 9,000), but you could also take an in-person cooking class from Chicca, a Sicilian who’s made Tuscany her home for many years now, or go on a bike ride. We’re scheduled to spend a week there this fall. This is definitely off most people’s Tuscany radar: http://tuscanfoodtours.com/about-us/

Thanks everyone for your advice and insight. For those who have traveled to Livorno, how was your experience here? I realize that April may be chilly, but I'm more interested in looking at the sea rather than swimming in it. Are there many options for sea view dining? I understand there is a series of canals. Are they picturesque or mostly for industrial use? Thanks to everyone for taking the time to respond.

I have not been to Livorno, but I think that would be a good choice for April unless you want super quiet like a village would be.
I heard about Livorno on this Italian food show:
https://www.imdb.com/title/tt4485678/
And here is an Italian food blog overview:
http://www.emikodavies.com/tag/livorno/

Since you are traveling by train and headed to Lucca/Pisa after visiting central Tuscany (Florence/Siena area), I would recommend either Castiglioncello or Quercianella, both just south of Livorno and served by the train with the station walking distance from the water.

https://www.hotelcostadeglietruschi.com/en/castiglioncello.html
https://www.tripadvisor.com/Attraction_Review-g1439320-d10767524-Reviews-La_Spiaggetta_Quercianella-Quercianella_Province_of_Livorno_Tuscany.html

Viareggio or the more upscale Forte dei Marmi are also popular destinations, both north of Pisa and also easily reachable by train.

They are somewhat larger towns on a flat area of the coast called Versilia, so that beaches are sandier, but I prefer Castiglioncello and its rockier beaches.

However in April it is still early for beach time or swimming, so if you are looking for more vibrant life, restaurants, etc. Forte dei Marmi or Viareggio will definitely offer more than the much smaller Castiglioncello or Quercianella

Take your pick.