6 am international flight out of Venice, but airport opens at 4 am

Venice to Paris is NOT considered international - it's all Europe.

We always book private taxis in advance, esp at that time. Your hotel can do that for you.

Sorry I can't answer any of your other questions

Venice (near Mestre). This is confusing. Are you in Venice, or in Mestre, which is on the mainland?
If you're in Mestre, it's probably easiest to take a taxi. Have your hotel arrange it.
If you are in Venice, does your hotel have its own dock, or do you need to first walk to the nearest one? A private water taxi at 3 am should definitely be booked at least the day before. Your hotel should be able to arrange it.

Flights between Schengen countries are considered domestic ones, so 2 hours is sufficient.

We are staying in Mestre. I apologize if I confused you. I was told Mestre is a borough of Venice.

I don’t know if the hotel has its own dock. I will figure out if I can send them an email to ask.

I was told Mestre is a borough of Venice.

Not really.

Venice has Sestieri- not boroughs- and Mestre is a city on the mainland- across the bridge a good ways from the island/cityof Venice.
You are not "staying" in Venice at all.

From Mestre you can just take a land taxi to VCE about 15 min? - there is no waterway from there for a water taxi to use.

Can you switch your hotel from Mestre to Venice?
You will have traveled very far to stay in a mainland suburb of Venice.

For better info, maybe share the name of the hotel. A number of people, including me, are confused exactly where you are staying.

If nothing else, "How can I get to the airport at 4 AM?" or 3:30 if you want, is a good question for your hotel. They may have options, including a private driver at a set fee they use. However, others on here might have experience with the area where your hotel is. If by Taxi, I would have them arrange it.

Venice to Paris is NOT considered international - it's all Europe.

Well, technically it is international, just no passport controls since they both are in the Schengen area (Some of Europe is not)

You are not "staying" in Venice at all.

Mestre is in the Commune of Venice, just on the mainland, not on the island. So legally, it can be considered Venice.

I feel a little bit silly now. It appears it’s all on land. And may not cost more than 20 euros via land taxi. Thank you for easing my mind.

The name of the hotel is The Plaza Mestre. Thanks for all the responses. This is a great group and I’m a newbie for posting for advice. Eternally grateful to you all. Thanks!

Now that you have worked out how to get to the airport for that silly o'clock flight to Paris, and how easy it is; I'll just mention how very convenient you are to being in Venice.

Your hotel is almost directly across from the entrance to the Mestre railway station which has really quick, really frequent trains right into the Grand Canal in the heart of Venice. Get on in Mestre, 10 or 11 minutes later get off at the last (usually only) stop of Venezia Santa Lucia and walk out to the front of the station. You will overlook the Grand Canal, the glistening water taxis and all the water buses - the magnificent vaporettos . And you can walk around - it is paradise.

We don't know how long you will be in Mestre, but there are loads of hints about enjoying Venice. If that's what you'd like, just ask.

1. As explained above, 2 hours are sufficient for a intra Europe flight.
2. If the hotel is in the district of Mestre, a taxi will take 20 min to get to the airport.
3. Maybe not the restaurants but the coffee bars will be open on time for you to have something before you board.
4. Not sure if you are in the historical center or Mestre, but it is a good idea to book a water taxi in advance. Vaporetti and Alilaguna are available at night but not sure how convenient their stops are for where you are staying. If you decide to go by water taxi you might as well ask them to take you to the airport directly. It’s about €120.

PS: Mestre is indeed a district part of the city of Venice, it is not a separate city. The City of Venice (Comune) extends in the mainland and includes both the districts of Mestre and Marghera, among others. The 6 sestieri are the historical subdivisions of the historical center of Venice.

The hotel is in Mestre - directly across from the entrance to Mestre station.

Will the airport lobby be open before 4 am for us to queue or will we need to wait outside? Typically for international flights we are encouraged to arrive 3 hours in advance.
We are staying in Venice (near Mestre). What time would we need to arrange for a private water taxi (30 minute from dock to airport) but what about loading and assuming picking up from the hotel?
Will any restaurants be open that early in the morning at the airport?
Should we book the private water taxi in advance? I believe the public transportation will not be running that early in the morning but please correct me if I’m wrong.<

You're staying on the mainland, across from the train station, you're about 20-minutes transit time away from the airport. Getting to VCE should be very easy and you're not traveling international, you're flying into Paris.
Restaurants open at 4am?!? You're kidding right. In all seriousness, a coffee bar or two that'll have pastries but, thats it (hopefully their morning delivery arrives in-time), otherwise vending machines.

I have been on the 6:00 flight from VCE to CDG. Two hours is enough. There will be people milling around waiting for the airport check-in to open. The terminal was open, just lacking the airline employees to check luggage, etc. Mestre is quick and easy to get to the airport all on land as you now know. As I recall there was not much open at the airport that early.