Hi,
On page 3 of the RE wizard, you can select the columns you wish to exclude from the RE process. You will have to do this for each table and column you wish to exclude.
Unfortunately there is no way right now to have all the generated tables extend a given common superclass – that will have to be done by hand for now.
I will ask the DB team to add the ability to specify a common superclass during the RE process so all classes generated would automatically extend that class; this should be available in a future release.