You can be as secretive or open about your characters as you wish. Just remember your groups are opposed so that information can and will be used against you
Also please don't feel like you have to make your character fit the mold of your group. You don't have to be evil to play the role of an antagonist. You don't have to be happy about that role either.
Re: setting. We have no concrete place for the setting yet, other than it taking place in Forgotten Realms. More info will be available prior to us starting. Just remember we're writing this scenario ourselves so the planning stage may take a little longer. We have a skeleton setting right now, lacking in specifics.
Re: encumbrance. I've never played a dnd campaign where the 'rules' were in place for things like carry capacity, hunger and exhaustion. Dm discretion will apply but, to give a rough understanding, you can carry as much as a typical rpg hero. A lot more than you could feasibly ever get in a backpack, but not enough to fully furnish a bungalow.