How would Harry react when Lucius kidnaps him? How would he fight back?
he'd fight back, but after a while, I think he'd try and figure a way to get the best of Malfoy by using words. He can be tactically astute at times. In the Ministry, he keeps Lucius talking whilst instruction the others to smash the prophecies.

Harry's a fighter, how would he react when Lucius tries to persuade him to become a believer in blood prejudices?
OH, I can't see him caving there at all. I honestly can't see Lucius trying to convince Harry either. He must know it wouldn't work. Frankly it's OOC for Lucius to try to persuade him.

Could Harry be Obliviated easily? Do you think this is realistic and has a chance of happening?
You can Obliviate someone when they're not conscious, (see DH in the cafe - Tottenham Court Road) so if Harry were Confunded, then he could be Obliviated. You need to be careful here, though. If he's Obliviated, then his memories won't return. Lockhart never recovered. Hermione didn't use Obliviation on her parents. Instead she modified their memories, that's how she was able to restore them.