I have visited Vung Tau for several years now on marine business.
There is no weight restriction for luggage on the ferry to Vung Tau but just be careful when boarding with heavy cases as it can be dangerous.
Use the local labour and tip them 1 US Dollar or 30,000 dong but keep an eye on your luggage until it is on board.
Watch out for the taxi touts when you arrive at the terminal and agree a price to destination first as it saves any problems later.
I am going back to Vung Tau in May and if you have any other questions you need answered just let me know.
There are plenty of good places to stay but depends on your budget.
I have stayed in the Rex Hotel , The Petro House ( very reasonable ) uses to be used by the Russians during the cold wae and i currenly stay at the Imperial but rather pricey.