Okay.
First, know that this can vary from GM to GM. I'm only telling you what I perceive to be the most commonly accepted answers.
1) Yes. Yes, yes and yes. The restrictions being
- Some things are less probable than others, and thus harder to find. For exemple, a virus that can kill anyone in Amber save corwin might require centuries of constant Shadow Searching. And since the characters aren't aware of this fact, they could assume it's impossible to find.
- IMO, Pattern "negates" this sometimes, fixing certain things. So anything is possible, so long as it doesn't contradict the rules of reality as set by the pattern. This might be as light or heavy as you like. For exemple, this virus might be efficient in a given shadow, but utterly useless (and even impossible to exist) in Amber.
2) London to tatooine: Yes. Time depends on skill with pattern, psyche, stuff, and the relative "distance" between the 2 shadows, which depends on their similarity: It's faster to go from our earth to Jack Bauer's than to tatooine, for exemple.
Japan to spain: Heavily GM-dependant. I'd say probably no, since shifting shadow would still have him in Japan, and going to a shadow where he's instead in japan, then coming back, might require more time.
Going between places: Sure, but you gotta exit the shadow and go far enough, then come back.
3) Stronger than corwin: Sure. Check n°1. Shift Shadow: Sure: There are creatures able to do it, so no problem here. Walking the Pattern: I'd say no. Unless one of them happens to have Amber blood. In fact, IMO, Pattern "reduces" probabilities to a set number of facts, thus countering the shadow's chaos-based infinity.
4) Mostly no. IMO, it might be possible inside a given shadow, but, outside, time has still passed (You exist the shadow after you entered it), or it is "false" time travel, where you in fact shift shadows (This is my favourite answer).
5) Depends heavily on GM's judgment. I'd use psyche as Strength lifting capacity for this.
6) Getting Pattern without walking it: No. With walking it: Yes, sure! You walk the pattern, and then spend the points/take bad stuff. If you don't, you don't know how to do things, although you might learn. Most GM use Partial Powers to simulate this: You buy shadow walking, curse ability, Hellriding... as separate abilities.
7) Hard. Very hard. But not imposssible. Trump trap: yes you can. But he has to fall into the trap, you can't just wave it at him
. And a lot of things can block your trump trap, beginning with a simple power word.
It doesn't block it. It's just that physical laws vary from Shadow to Shadow. The more diverse, the more so. That's why in Star Wars shadows, there are sounds and explosions in space, and not in Shadow Earth.
So, if a given spell requires water to boil at 100°C, while in another, it boils at 110°C, your spell won't work.
For your shadow exemple, these are sufficiently close that your spell would work without problem.
9) He gets grayswandir. How? What happens if, say, eric was holding or seeing it? Well, I'll pass