Venice, Cinque Terre and Florence

For a similar trip, I did not require a car. There is perfectly adequate transportation in each of these locals. For my preference, I would consider an extra day in Venice, one less in Florence. Folks will tell you not to visit Cinque Terre. Ignore them. Enjoy.
If you had more time, I would suggest staying elsewhere in Tuscany (an Agre Turismo) and renting a car. A car can really expand your options.

I'd spend more time in Venice (jet lag recovery) and yes as prior poster noted, I suggest skipping CT (it's just a long way out of the way for possibly iffy weather in April). Whatever you decide, be aware of the ZTL in Florence, I'd suggest not having your rental car in the city proper https://www.visitflorence.com/tourist-info/driving-in-florence-ztl-zone.html

Having just been there, I would suggest considering a location other than Cinque Terre - this is based primarily on how it doesn't fit the rest of your itinerary, as well as the belief you can find experiences equal to or better closer to Venice and Florence.

You might consider extending your time in Venice and adding a day trip or two - there are numerous suggestions here on the travel forum:

https://search.ricksteves.com/?button=&date_range=1y&filter=Travel+Forum&query=Venice+day+trip&utf8=%E2%9C%93

Your basic approach to Florence looks good, and you can also search here to get opinions on where to pick up and drop off a car. Siena is an obvious choice once you're in Florence.

Since you’re flying home from Venice consider going to the Cinque Terre on arrival day. This involves taking a taxi to the Venice Mestre train station and a train to Milan’s central station where you need to transfer. From Milan take a direct train to Monterosso and sleep there.
I don’t recommend renting a car in Italy unless visiting the Tuscan countryside and Sicily. Furthermore, you need to be savvy on ZTL zone laws if you do rent a car. Once you’re in the Cinque Terre you have no need for a car. You do not want a car in Florence.
I liked the Cinque Terre but I went in Mar 2005 before the crowds arrived. The weather was in the low 70s and was almost too hot for hiking. If you do hike add an extra night.
I agree that three nights is better in Venice and four nights in Florence is all you need. Buy tickets for the Uffizi Gallery two months out to guarantee a reservation.
If your flight departs Venice early morning a water taxi to the airport will cost over $100. Your other option is to sleep near the airport the night before flying home.

Two nights in Venice means one jet lagged day. Not worth doing.
You can train from Venice to CT. Takes 5 or 6 hours.

Consider splitting the time equally between Venice and Florence. Each has more than enough to keep you occupied the entire time, and you will not be as rushed. Think about flying into Venice and immediately taking the train to Florence. On your arrival day you will be jet lagged, so that makes it a good good day to get your additional travel out of the way. After Florence and Tuscany, go to Venice and finish up there.

To see some of the Tuscan towns, consider taking a local day tour(s) from Florence. That will eliminate the need for a car and allow you to just sit back and enjoy.

Just food for thought.

If you are locked into RT Venice you might consider heading right to Florence on arrival. That last night at Venice airport is a waste of a day and night.

Arrive VCE
Bus or taxi to Venezia Mestre- catch fast train to Florence 2 hr 15 min.
Florence 6 nights.
Keep your day trip options open in Florence depending on weather/stamina, etc, You can easily day trip to Siena or Pisa and Lucca by train- no need for a car.
CT is not really a good option as a day trip.

Return to Venice- 4 nights
What time is your departure flight? While it is more difficult to get to VCE for departure it is not impossible, just takes some planning.

Or you could do
Florence 5
Venice 5
Both have many easy day trips

ETA: AH! see TC has same idea.

hey hey NaomiJoy
where are you flying from to venice? I would spend an extra day in venice taking one day away from florence or think twice about cinque terre. like others say out of area with 5-6 hour train ride.
are you doing multi-city (into one city out from another)? your 2 days in venice, first day will be “fuzzy”, jet lag is real. leaves with one day.
also remember check-in is 2-4pm, check-out 10-11am, if renting a car, you will need an IDP per driver, search AAA.com for info. you could take train to florence first, spend your 4-5 days then train to venice and spend your 2-3 days and close to airport to depart. search your transportation there to airport, many flights are early, like 6am. europeforvisitors.com great info
it will be busy and crowded in big cities you’re visiting since it’s Easter and spring break. see what attractions/activities need pre-booking and when dates/time slots become available. good luck
aloha

We were thinking of spending the first 2 nights in Venice, as from what we heard, 2 days there is enough

That will not give you '2 days'.

When in April is the trip? The earlier in the month, the greater the likelihood weather at CT may be not so welcoming.

2 nights in Venice, as from what we heard, 2 days there is enough

Sure hope you are not taking investment advice from them.