1) The train station in Brussels airport is at the lowest level. You can catch a train there to Brussel Centraal. Trains run very frequently (about every 10 mins.).
2) Yes. You buy your tickets at the ticket counter in the train station area. It's impossible to make an advance booking for a commuter train.
3) It's certainly not too much time, but it's okay. Gent and Antwerpen are about equally large but their centres are pretty compact.
4) -
5) As far as I know there are no Starwood/Marriott properties in Antwerp.

If you are going straight from the airport to Antwerpen, you don't have to travel to Brussel Centraal first. You can catch a train to Antwerpen (change in Brussel Noord) at the airport. You can also take the Antwerp-Brussels Airport Express. It's a direct coach service that runs every hour to/from the city centre of Antwerpen. The coaches leave from the back of platform B at the bus station (level 0).

Having done basically what your doing...in a different order. I would suggest you stay closer to the center of Brussels. The Marriott is very central...can't get better than that. Also it's within walking distance to the central train station..a little up hill so you can take a cab if you like. You don't need reservations for the train. Just buy it at the station. I would since your going with your mother...stay overnight in Brugge and do Ghent as a day trip. There are some great B & B's there.

Thank you Myriam & Monica.

We will be going to Antwerp straight from the Brussels airport.
The express bus you mentioned, do we get on it right from Brussels airport, or do we need to get to the bus station first? And how long is the journey?

Monica, I read that Brugge is very charming and quaint at nite and in the morning when it's more quiet without the tourists, but I have a really good deal at the Marriott Ghent and so I thought we'll stay overnite in Ghent and do a day trip to Brugge.

Bruges as a day trip is fine. It is touristy during the day, but it isn't like you are going in the height of summer, so it shouldn't be that crowded. And, like most places, people tend to flock together in the most popular areas of a city. It is very easy to find areas of Bruges that aren't overrun, even on a sunny summer afternoon.

Brugge IS charming at night and in the morning but since the train trip there from Ghent is only about a 1/2 hour you can easily arive early and stay late. Use taxis to and from the stations to save some time, although the distance from the station in Brugge to the historic center is not too far. When you arrive in Brugge, there will be taxis waiting just outside the station.

There are no Marriotts in Antwerp. I stayed at the Hilton which is very nice and well located. Great concierge lounge.

The Ghent Marriott is very nice and also well located. No concierge lounge but they give you vouchers for a free drink and appetizer each day if you're CL-eligible. I was upgraded to a Jr. Suite.

The Marriott in Brussels is much better located as opposed to the Ren. Also, a very nice hotel with a good CL.

I know there are people who believe Brugge can be seen in a day but I spent 3 nights there and still didn't see everything I wanted to... and I go, go, go all day long!

Have a great trip!

The Antwerp-Brussels Airport Express leaves from the airport.
From Brussels Airport's website: The bus station is located on level 0 - one floor down from the arrivals hall - and can be easily reached by using the escalators or elevators.
Centrally located on the bus station there are three platforms each with its specific use.
The Antwerp-Brussels Airport Express leaves from platform B.

The coaches leave on the hour, starting at 5 am - last coach leaves at midnight. Total travel time is 45 mins.

In Antwerp the bus has its stop at "De Keyserlei" (near Central Station). From there you can take either the metro (line 2 or line 15) to Groenplaats, which is the heart of the historical centre. I would strongly advise you to book a hotel in that part of the city. Hilton is on Groenplaats, very good location.

Do you have restaurant recommendations for Antwerp, Ghent, Brugge & Brussels?
I like bakery/cafe place for breakfasts, and anything good for lunch/dinner (inexpensive and casual). For lunch, I don't mind a quick grab & go type of a place.
TIA!

If you are looking for a good inexpensive lunch in Brugge, here is IMO a great find.

Den Gouden Karpel (Golden Carp) is one of Brugge's finest restaurants with prices to match. It is located in the little square behind the Vismarkt(fishmarket). However, in the Vismarkt square itself is a small take out shop also called Den Gouden Karpel so I would think there is a connection with the restaurant. The take out had prepared picnic containers filled with a nice sized portion of baked salmon, herring, tiny shrimp, tiny potatoes and veggies with mayo on the side. The young lady in the shop directed us to a lovely nearby park and on the way we picked up a couple of beers at a grocery that was just around the corner. We found a bench in the park and had an absolutely delicious alfresco picnic (yes I know that is redundant) made even tastier by the only 5 euro price per meal, the view of the ducks in the pond and children playing nearby. Since this was a few years ago, I would imagine the meal might set you back another euro or two.

For really cheap, the fries from the carts in the Grote Markt are great.

My sister and I spent 11 nights in Belgium in November 2010. We stayed 2 nights in Brussels, 5 in Ghent, 2 in Brugge, then 2 in Brussels again. It was a fantastic trip, and I'd go back in a heartbeat.

We really enjoyed Ghent (had been to Brugge in 2008) and found great places to eat there... Julie's House is a neat one with coffee, cupcakes and other sweets. It is near Gravensteen castle and worth the visit.

There are also really good french fry stands that make good treats (have to eat lots of fries, waffles and sample the beer). We especially enjoyed Frituur Jozef in one of the squares. The brown sauce was delicious!

And probably our best meal in Ghent (we ate 5 dinners) was De Graslei, right next to the canal. Great food, great service and wonderful atmosphere!

I know you've probably booked your accommodations, but for future reference, we totally LOVED De Waterzooi B&B in Ghent, my best stay in a B&B/hotel ever!

Enjoy your trip! Hope you do a report so I can read how you liked Antwerp. For some reason we never made it there...

Okay, some breakfast/lunch places in Antwerpen:
Den Boterham, Plantinkaai 14 (historical centre, at the river Schelde)
Den Artist, Museumstraat (south quarter, accross from the Museum of Fine Arts) - http://www.brasseriedenartist.be/nl/x/29/ontbijt
Boon, Leopoldplaats
Café Imperial, Meir (shopping axe)

There are numerous places for lunch, but these I know from own experience.