Harry Potter and the Goblet of Fire - plot hole?

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Spoiler alert, just in case anyone needs it.

I'm a bit late to the party but have read the Harry Potter books and now working my way through the films.

In Goblet of Fire, why does Crouch jnr go to the effort of putting Harry through the Tri-wizard tournament and helping him win (which was not even guaranteed to succeed)? He could have made anything into a portkey and got Harry to touch it with so much less effort. Or am I missing something???

Yes, that's always bothered me. Can you imagine the terrible literacy on display in that school?

Plot-wise, Order of the Phoenix bothers me more. We see the silly, months-long plan to get Harry to take the prophecy so Voldemort doesn't need to risk showing himself by getting it himself. If Harry had travelled properly to Grimauld Place to check Sirius' whereabouts instead of doing the head-in-the-fire trick (or used his two-way mirror), it would all have fallen apart.

And yet look how easy it is to get in undetected! That big group of death-eaters - including the ones escaped from Azkaban - are already there waiting. You're not telling me Voldemort couldn't make himself invisible (as Dumbledore was able to) to get in the same way Bellatrix did, undetected, and get it himself.

The books also explain voldemorts past much better than the films and dumbledores early friendship with grindlewald.
from what I can remember the films doesn’t mention Tom riddles family tree which is really important for the plot

But why did she need to be teaching? She could easily have lived there in a non teaching role, or gone into hiding like everyone else. Dumbledore had infinite money and a wide network of allies, surely he could have hid her somewhere that didn't damage the (already shakey) education of hundreds of kids.

I agree Voldemort wouldn't want to get involved in that directly because he wasn't exactly a honest kind of guy himself. They could have set up a system where you pledge to one other death eater you will always obey mouldy Voldy or everyone promises to Bellatrix though. She'd be happy to do his bidding.

We see the silly, months-long plan to get Harry to take the prophecy so Voldemort doesn't need to risk showing himself by getting it himself.

My understanding is that the Black torture hallucination was a late thought, in the run of the school year. First, Voldemort was pondering how to get into the MoM (hence the dark corridors), then he realised his connection with Harry, presumably a bit after Harry saved Arthur's life, then he started to use it for his own gain after a while of trying to shut Harry out. It makes a lot of sense. The time pieces less so, you cannot tell me that in a political world like the MoM where a school girl nonetheless is given one of the most powerful devices given to wizardkind for educational purposes no one has attempted to change the past? I am talking about the 7 books here, I am aware that TCC is trying to address that one (but I have never read that in full).