How to get from the Venice Airport to the Santa Lucia Train Station

You can take the Aerobus from the Airport to Piazzale Roma (which is located right next to the station) and walk from there.
Or if you want you can take a taxi.

There is a high, long bridge between Piazzale Roma and the train station. My travel mate didn't want to have to deal with that bridge when encumbered by luggage (I wouldn't have enjoyed it, either), so she took a vaporetto one stop from Piazzale Roma to Ferrovia. If you're going to buy a vaporetto pass (very often a smart financial move) that little vaporetto hop wouldn't cost anything extra.

Does the Aerobus depart regularly? Our plane doesn't arrive until 6:30 pm and I have no idea how long luggage and customs will take. I'm assuming it will still be daylight when we walk to our hotel.

The line 5 Aerobus runs from 4 something AM till about 1 AM at night. Buses are every 15 minutes, except for the very start of the morning, or after 9pm when they run every 30 min. So if your plane lands at 6:30pm, at that time there will be a bus every 15 min.
Daylight or night it doesn't matter in Venice, there are millions of people walking at all time, and the vaporetti run 24 hours a day (at least the main lines).
Just locate your apartment on Google Maps and use the Street View function to become familiar with the walk. The way addresses are organized in Venice is baffling even to local mail carriers. Numbers are based on each Sestiere (district) and increase from a central focal point in the district in concentric circles departing from that focal point. I don't think one could come up with a more complicated way to number home addresses in a city.

In this image, you can see the pedestrian bridge (on the left of the image) which connects Piazzale Roma (on the right where the buses are) to the Santa Lucia station, which is on the other side of the bridge approximately 500 feet after the bridge.

One suggestion - buy a paper map at the Tabac at Marco Polo. Phone maps can be problematic in Venice. Best four euro you will ever spend.

The Calatrava bridge from Piazale Roma to Ferrovia is not too hard with luggage, although slippery if wet.

Roberto, is that crazy lift and balloon shaped gondola carriage still in place on the Calatrava? I thought it had been demolished.

It was there in 2018. Have no idea if it's still there. Haven't been to Venice in recent years and actually never walked across that ugly bridge, just saw it from the vaporetto since I parked at Piazzale Roma. I can't believe the City paid 13 million euro for that piece of crap (including a couple of million for that ugly egg shaped gondola. They even had to replace the glass steps with stone ones a few years ago, given the number of people slipping and falling (and suing the City). It should be called the Cacatrava bridge.

Cacatrava. Oh, very good, very sharp.

The gondola on the bridge was gone as of September 2022 and it has not been resurrected.

Was in Venice last week. Can confirm, the weird lift had been removed.

As for OP's question, there are two bus companies that run the route between the airport and Piazzale Roma, between them there is little waiting time. Note that their tickets are not interchangeable between the two companies.

We have crossed over that bridge with roller bags twice with no difficulty (but it wasn’t wet).

Although I am not a fan of the Alilaguna, the boat is another option. This would be the Alilaguna Orange line to the Guglie stop which is behind the train station. It might be as close to the apartment as the Ferrovia, and they wouldn’t have to shlep luggage up and over the bridge, or (what is worse in my mind) onto the crowded vaporetto to ride one stop.

https://www.alilaguna.it/en/lines/lines-map

or (what is worse in my mind) onto the crowded vaporetto to ride one stop.

The No 1 boat originates at Piazzale Roma where the airport bus drops you, so you should be among the first to board and then get off at the next stop before all the train station passengers board. Nonetheless, 9.50 EUR per person is pretty steep for such a short ride, unless you are getting a multiday pass, in which case you might as well use it.

Taking the vaporetto for one stop from Piazzale Roma to Santa Lucia will save you only 3 or 4 min walk. The station is only 1000 feet from Piazzale Roma. It is literally across the Constitution bridge (aka the Architect Pedro Calatrava bridge, who designed it).

I highly recommend the ATVO bus from airport to Ple. Roma. It’s about 8euro and you can buy it online before you leave the states. Then you show your phone/ticket to the attendant next to the bus as you board. No fumbling to buy tix at airport. I’ve done this twice (solo traveler) and it’s awesome. Try to sit behind the driver side for cool views on way into Venice. The ATVO schedule is online. Very frequent.