We did this trip 3 weeks ago!
2 large suitcases and 1 carry on (plus my back pack and DW's large handbag).
We used standard class train, but ensure you get the Inter City Direct train, as it is non stop to Rotterdam Centraal. We 'tapped in' and 'tapped out' using our debit cards and the cost of €14.50 was showing on our account next day.
We are both in our mid 70's and DW has a few health problems so needed help to get on the train. As I lifted the two large suitcases on to the train at least 2 males and 1 female helped me lift them on (the door level is higher than platform level). We did not take seats, although several people asked DW to take their seat! We waited in the door area with our bags for the 30 minutes direct journey.
On arrival in Rotterdam Centraal, we were again assisted by commuters to dismount the train.
When you arrive to the Main Foyer/Shopping/Food area of the station, keep the platforms to your back, and go to the right side. The Marriott hotel is just across the square - an easy walk.