|moon glum RPG Superstar 2015 Top 8|
Yes. A swashbuckler can use opportune parry on their turn. They can make an opportune parry whenever an opponent makes a melee attack against them (provided they have the panache, and an attack of opportunity to spend).
Yes. A swashbuckler can riposte on their turn, since an immediate action can be taken at any time (not just on a creature's turn). It costs 1 more point of panache and their swift action. (When you take an immediate action on your turn, it counts as your swift action for that turn).
Note that means that you can then take another immediate action after the end of your turn (though that counts as your swift action for the next turn).