Pretty much all of my information here is geared towards the state college level. If you want to go to the fancy expenisve ivy league schools like Oxford and Yale then a lot of the rules and reg's become much more complex and all sorts of hoops show up that you need to jump through, as you are competing against the whole of America then instead of people mainly from one state.
The requirements for my college international student program are available in detail
here for bachelors degrees. Basically they need proof that you can pay them for the first year, transcripts of all of your high school and any college school classes that you did in english and proof that you are competent in the english language (which can be shown on any one of several different tests). The ACT and SAT are two of these tests, and taking one of them can certainly help you to get a spot, but they are not necessarily a requirement. As an entering freshman they also require at least a 2.5 GPA in your classes.
As for AP classes, they aren't a requirement for enrolling. Basically all AP classes do is let you get done with your first year or so of college while you are in high school, therefore giving you more class slots to take classes that you want to take instead of the required ones. It is perfectly possible to get by without AP classes, and the majority of students will not have taken them when they enter your average state college, to the point where most college plans are designed for people who haven't taken them. If you do decide that you want to take any, I suggest checking around to see if you can get any of the many supplementary textbooks that people design for AP tests. When I was in high school, for example, I purchased both an "AP Calculus Testbook" and a "AP Physics Guidebook" both of which were written by independant authors and are designed to teach you the material that is tested without all of the extra stuff companies like to stuff into normal textbooks.In regards to taking the actual test itself, I believe that many AP tests offer ways to take them in your respective country, but I am unaware of the exact requirements and things that you need to do in order to do so, so you will need to find that information elsewhere.
6)Colleges want to know that you can pay them most of all, after that they tend to look at your GPA and a little bit at your SAT scores. In order of importance: Money>GPA>SAT, with them not really caring at all whether you were involved in school events or sports in the slightest. The fact taht you can pay them is the most important, with the fact that you have a good GPA (and therefore will stay in school long enough to pay them even more) is the second most important.
7)If all you want is an associates degree, then community colleges are fine. However if you want to go into the more competitive fields such as computer science or engineering a bachelors degree is almost a prerequisite. As such it is fully possible to go to a community college for two years, then switch over to a normal college for the last two years, but most universities smile more favorable upon students that come to them for all four years then students who transfer in halfway through. For costs the current estimated cost for normal international students is $35,700, with additional costs being required if you are unable to pass the english proficiency tests they administer. It is possible to get reductions in this number however, along with financial aid and other reduced tuition rates. Combine that with the fact that that cost includes both housing and food and if you find a place off-campus to live and shop at nearby stores and then cook your own food as opposed to buying their expensive meal plans you can probably cut a couple of thousand dollars off of that number. Of course the first semester you will probably end up living in the dorm (it being difficult to swing a lease from a foreign country), it can become cheaper once you are in your area and you can look around for better deals then the overpriced college ones. All-in-all I'd say that if you can afford it go for the four year plan, simply because it will be both easier to get enrolled into the college system and you will have more time to get to know your professors.
For green cards and visas I believe that once you are actually accepted to a college it is a fairly simple process to get the visa issued, it just is a lot of rubber stamping and other paperwork for the sake of recording everything regardless of the fact that you have basically already been accepted. I'm not 100% on this though, only knowing about the process from what I have heard from some of my friends from foreign countries.
Lastly american companies (at least in my area) try to hire american if they can, though part of that is because my state shares a border with mexico. Regardless of their opinions, going to college here in america is a huge bonus to your chances of being hired, as it's not uncommon for companies to hire students right out of college to come work for them. You can also greatly help this process along by getting to know your professors at the college. Most of them know people in the industries who are looking for new college students to intern or hire, and a good letter of recommendation from one of them can do wonders to getting jobs. One of the biggest things for getting jobs right out of college is who you know, and it's not uncommon for professors at colleges to be the one to set you on the way to your first job.
While going to a college an upper college does help, going to a state college can be almost as good and can be significantly cheaper to do. There are usually enough openings in many of the more popular fields such as engineering and computer science to take a large portion of state universities as well. There are even some companies out there that specialize in "new blood", hiring students out of college and keeping them for a few years, at which point the students leave and move onto other companies now that they have some experience.
Also 4-year degree≈bachelors.
Basically most college 4-year-degree programs are basically a program that is streamlined to get you your bachelors degree while making sure that you know everything you need to know. As I mentioned earlier it is technically possible to go to a community college for two years and then do a two year bachelors program at a university, but most universities prefer it if you go the 4-year route because not only do they not need to worry if you have actually been taught everything you need to know, but they get paid more as well, which makes them happier. As such often the amount of paperwork that you need to go through is larger if you do 2&2 instead of 4, but it's spread out over a longer period of time.
Woah, lots of text here, but this is most of what I know about the way that the state level of college works here in the U.S.