the critical strike option is on the combat menu that comes up when fighting - its with flurry etc. - you just have to scroll through them til you get the one you want to use.
as for bastila - put her on jedi support and give her party buffing powers and heal etc. If she is on jedi support she will automatically cast her powers before attacking anything so you can just leave her too it while you take advantage of the bonuses from the buffs. In fights you can leave your party members to do their own thing and they will follow the script you have set, like jedi support, ranged etc. and then you can choose to switch to controlling them any time you want just by clicking their icon if you want them to do something specific.
as for party members - canderous and carth are great as back up with ranged weapons (or even melee for canderous). I usually have one ranged party member or droid and one jedi with me when I play - unless I feel like a change then I go for all jedi

If you have one ranged and one jedi on jedi support doing all the healing and buffing stuff, you can pretty much leave them to it most of the time and concentrate on your main character in fights.