So I'll answer your first question.
I wouldn't say he's terrible- his problem lies within the fact that generally speaking he has an "Odd" requirement in order to "perform".

He has the potential to be a stronger Jonin Minato while simultaneously being a weaker Joinin Minato, see in order for his Mystery to Interrupt the whole entire line up he has to hit someone who is tagged, the requirements for meeting that are huge due to the limiting factors in place, eg There's not a lot of other Ninja that tag, he himself tags but tags a random target, not necessarily the target you want to hit, most people use Immunities. Mean while Jonin Minato just interrupts everything with his bond Mystery & has two chases that allow him to scale, instead of an "Action" & he can reset his own mystery.

That said, he's usable, he's great as a 2nd slot Ninja personally, assisting in damage right after the mystery of an Angel Konan for example that Tags an entire line up.

Now for Line Ups, due to the fact that he can't chase you end up with line ups with incredibly short chases & I don't like that.
There might be more people that can help you on the line up front- I personally just find it hard to make something "Good" & if it's not at least "Good", I see no reason to honestly post/utilize it.

On your question about Wind Main being weak, indeed she might get slapped around- that's what Kurenai is there for, to try & mitigate it, if you're having serious problems you can utilize Flower Guard to give them both a shield & Immunities at the sacrifice of damage.

Iruka provides a little more defence through shields, seeing as your Gaara isn't skill broken- you also don't have the added pain that your Barrier will be cancelled with Iruka you might also pull of interrupting someone else's barrier.
On the other hand Gaara can straight up cancel an enemies barrier & he can still provide some shields.

I would go for collecting Angel God Konan, but I'm not completely experienced in the use of Hokage Minato, so with that there might be a better line up that I personally don't know about that may utilize him better but generally from what I've seen, yes AGK is the way to go.
You also don't have to use him in a secondary spot with AGK, you can in fact round 1 an AGK if you're lucky & you can base your team around that possibility.