There are funerals devoted entirely to prayers for the deceased before burial. If you ask such people, they will say the funeral is for the benefit of the deceased. One may speculate that it also meets some psychological need of the living, but I have no real information that would lead me to think so myself.
When a funeral becomes "a celebration of the life of" the deceased instead, it's very clearly for the living.
Funerals are for greedy undertakers who charge ridiculous sums of money when relatives are at their most vulnerable. My Dad would have had to use up most of his savings just to cremate my Mum until the rest of the family helped out. I would rather be chucked on the compost heap at the bottom of the garden and if your garden is big enough in the UK you are allowed to be buried on your own property.
Most people would have no idea what to do anyway. I can't see anyone 'Googling' it to go ahead with a DIY burial. I suppose in the UK there would be some sort of punitive tax to stop anyone doing that in the first place. Then they would get you for polluting the ground if your relative happened to have mercury fillings. Basically they will make it very difficult.
No. I haven't read a single book of it, though I've seen two movies (the Philosopher's Stone and the Order of the Phoenix). Frankly, the universe isn't all that interesting, especially with the LotR ripoffs by the fifth movie.
Yes, but not all the living. I don't think they've ever really "helped" me except in cases where I barely knew the person, and the idea that people gain closure at them is sort of absurd to me. Actually, the idea of 'closure' itself isn't really something I'm sure I'm on board with. I need different narratives. The common ones about loss and grief don't work for me, I guess.