q1: this depends on the type of caster.
A spontaneous caster (sorcerer etc.) needs a full round action to cast the spell enhanced with metamagic. In the surprise round, you have only a standard action.
You could start a full round action, and if you act in the first round (the round after the surprise round) before the opponents you attack, they will still be flatfooted. Otherwise, no sneak attack damage.
Of course, if you prepared a Split Ray spell (wizard, etc), no extra casting time is required.