The quick answer for how much land to give them is as much as you can! There are loads of topics on the forum about this, however in my opinion, you should give them enough space to have time together, time apart, somewhere to sleep, somewhere to eat, somewhere to use as a toilet and somewhere to drink, so nothing gets too over used! The look of the field at the end is dependent on the weather, their food (as they may feel less need to root if they are full up!) and the amount of space. It is really up to you - 100m2 is probably the minimum.
With regards to the gate, I'm not really sure what you are asking. If the gate is to keep things out of the ark, it needs to be the whole height, as wind, rain and other animals would be able to get over the top. If it is to keep the pigs in, I think this will be ok.
However, would it be easier to have no gate, just face the opening away from the wind and rain (perhaps in the shade), meaning the pigs can go out and in as they please.
Hope I helped!
Cheers, Nic