This won't be the best grammar explanation ever, but here's my try: This is just one sentence, not two; the second part is a dependent clause where the new subject (the defiance) and verb (giving way) depend upon the first part to make sense. This is a common thing for me to do when writing is have a statement, then elaborate with another clause using the -ing form of a verb. You may see something like this: "I ran out the door, grabbing my keys on the way." Hopefully this makes more sense knowing that the second part isn't missing a verb. As for the use of enchanted, the way I'm reading it, it's actually functioning as an adjective, just in a way you wouldn't normally see it. Consider replacing it with other adjectives: "I stood there happy." "I stood there baffled." Enchanted isn't modifying the verb but rather the subject. At least, I think so. A second opinion would be helpful.

Haha, you can, but it's informal and has a bitter connotation to it. "Down the tubes/drain" is a bit more neutral but still informal. It sounds like in the context you're giving it would work, although I wouldn't if it's for an academic paper or work report or something like that.

It means moving something so that it covers more area. If you spill milk, it spreads, you spread peanut butter over bread, disease spreads, responsibility can be spread among more people, and so on.

It depends on what you mean. If it stopped working, like Mohamed said, it would be, "our computer system is down." If the system has been replaced with another system, you could possibly say it's expired, but only if it's meant to be funny because that's how it sounds. Otherwise I'd say "our old system has been replaced." Similarly, if the system has actually expired-expired, as in died and will not be functioning again, you could also say expired if you're trying to be funny. Otherwise, one more formal option is "our computer system died. We'll need another one." If the computer system you're referring to has a subscription it depends on in order for you to use it, and the time has elapsed, this would be a non-funny, completely legitimate reason to say "the computer system has expired," although to remove any confusion I'd say "the computer system subscription has expired."

I wouldn't think there's a difference in difficulty for the two accents. It really depends on what you want - what you feel a connection to, and what's practical in terms of where you want to live or who you'd be speaking English with. I personally think both have appeal, although I think most people would say the British accent is better, haha.