When in “early spring”?
Things don’t really open up on Amalfi Coast til closer to mid April. Weather is iffy then and water is cold. Easter is 3/31 so you could avoid that week.
Positano is not really a “beachy” town. The beach is tiny and pebbly. It is a very steep town with thousands of steps and stairs.
There are direct fast trains from Salerno to Florence- about 4 hours- you would take ferry (if running) from Positano- change ferry in Amalfi then to Salerno. Train station is close to ferry port. Other option is bus- slow- or a private driver.
You’ll likely want to get going so a fast train in the am might mean you need to stay in Salerno night before.
Rome needs 4 nights
Positano needs 4 nights- since it’s a trek to get to and from
Florence needs 3 nights-takes half the day to get there
Tuscany town - most will need a car- 3 nights
There’s 14 nights right there- I think you’ll need to add a few nights if these are places you want to see.
Count your trip in NIGHTS- you'll get a better picture of how itinerary flows.
A 2 night stay means you have 1.5 days. Every time you change location you lose a half a day,
If you can fly IN to Rome
Rome 4 nights
Train to Florence 2 nights minimum
Pick up car- Tuscany town 3 nights
Return car in Florence
Train to Salerno then to Positano 4 nights
Naples 1 night
Fly Out of Naples
You will need to stay in Naples the night before your flight so that’s 14 nights.
Have you poked around Trenitalia to see your train options- use same day of week in the next few weeks to get an idea of train schedules.
Be sure to use the Italian station names
Roma Termini
Firenze SM Novella
Napoli Centrale
Salerno
Have you been to Italy before?
Amalfi Coast usually best saved for a 2nd or 3rd trip- it's a great area but transportation there is a pain