2. Can you move back to Camelot for your heroic action and not do anything? (even if there are siege engines there) Can you just stay there until your next turn to collect more white cards?
Slightly confused by the question, not sure if poor wording, or you missed a rule somewhere.
Spending a Heroic Action to move is the -entire- Heroic Action.
Spending an Action to move back to Camelot -is- your turn, you may not Fight or Draw on that same turn (unless you spend a Life Point to take an extra action).
On your next turn you are free to Fight or Draw if you wish.