There is a safety bar than runs to the concourse on some levels, this makes the seats restricted viewing but it isn’t really, you won’t have a problem.
Your link doesn’t work but what you’re quoting never happened, don’t know of any cases where this happened, the EU are soft on immigration, whether legal or not and no country in Europe wants the migrants, they are happy to move them on.
Wembley station is the closest to the stadium but that is overground but the closest tube station is Wembley Park which is at the other end of Wembley way.
Facilities are the same, better view, not the best closest to the pitch, I’m going to try and get category 3 as pretty good view from there but you do share the same facilities as the lower categories. Top tier won’t be open for this game.
I expect about 18k Vale and 14K Mansfield. 30k is about the norm for 2nd division finals. Booked my train and hotel for the first night., hotels are looking very expensive that weekend in London.