1 & 2: XD me neither. I'm pretty good with editing wikis, but aside from that I'm not quite an expert in anything computer related, really. (I don't even have a clue if it's possible to make screencaps from a DVD, But I suppose it should be) But you can look it up to watch any of the movies online, and make screencaps from them there. Although, it depends on what kind of computer you have on how to make the screencaps. If you have a windows computer, you have to hold the windows key on your keyboard, and then press "Print Screen SysRq" or anything similar. But if you have another kind of computer, I have no clue on how to make screencaps on it.
3: Well, I just tried to add any images related to The Jungle Book: images found on google, screencaps, official posters.....etc. So, anything really.
4: I sometimes take images from other sites too. But wether getting in trouble or not, I think depends on which sites you go to, and how you take the images. When I take pictures from another wiki or site, I copie the picture, paste in on my pc, and then upload it on the wiki. I think when you do it like this, no one will find out, and you won't get in trouble. And even if anyone might ever find out, I don't think there'll be trouble. (Although I'm not sure)
5: Well, I don't have any idea what might cause that, but if you're using the new FandomDesktop layout, it could be possible that it hasn't been updated yet for everyone to access that. If so, you can go to your prferences, and change it back to to old layout (Oasis), and then maybe you'll be able to access the Gallery of New Files.
But if you still can't reach it, you can link me the the wiki, and I can open the feature, and then give you the link.