I'm sorry no one has commented - I don't have any experience with geese so hopefully someone will come along who can help.
1) With chickens, I tend to put them into lockdown on the evening of Day 18 when most people say Day 18/19. I think it doesn't matter too much as long as the air cells are progressing on schedule and they haven't internally pipped - many folks monitor for the internal pip and then lock them down. With chickens and ducks lockdown times can be flexible and an extra day or so won't cause any negative effects.
2) With chickens, I've found humidity best around 65%-70% at lockdown. It usually increases when they start to hatch, but I've never had an issue with this. There are many opinions on humidity and it also depends a lot on how humid your house in terms of ambient humidity. You will have some trial and error figuring out what works for you. Though some people swear by it, I will never dry hatch or incubate - I've successfully been hatching silkie, cochin, black copper marans and ameraucanas without problem. I think this is especially important for waterfowl who are naturally hatched in more humid environments in the wild. Always consider the conditions they would be hatched under if incubated by a goose (or duck or chicken - depending on the eggs you are hatching), usually it is best to try and replicate this as closely as possible.
3) Most people will hatch them horizontally, but if you are really worried about air cells, some folks swear by hatching them upright with the air cell up (of course) in cartons. Just make sure the egg can breath and that not too much of the side is touching whatever surface is propping them up. For example, people will cut out the bottom of the carton - or just use the very base of it - to decrease the amount of carton touching the egg while still using them for support. I have never hatched upright (as my eggs have always looked okay on lockdown), so cannot tell you to which way I think is better.
