4) Why did Harry have to be the one to locate and destroy the horcruxes? I’m sure others (e.g. Kingsley, Moody et al) could have done a much better job.
5) The whole fourth book makes no sense. Why did (fake) Moody have to devise the entire elaborate plan of entering Harry into the tournament, and helping him every step of the way, and volunteering to carry the cup etc.? He could have skipped all of that and just turned any random thing into a portkey at any random time and he would have achieved the same result of getting Harry to the graveyard, with a lot less suspicion created along the way.