Each of your questions completely depend on the schools. The general requirements will vary, and whether or not you can take the courses at another school will vary in general. Certain classes MUST be taken at the 4 year school for it to count. You can look into specifically colleges and look at their transfer plans. Your best bet is to contact the junior college that you would like to go to, and ask them what kind of transfer plans they have for each of those majors, and whether or not they had something you could view online.
For example, if you are in California, try looking up the IGETC plan, some schools have it. It's a transfer plan that allows you to take classes that are accepted at a UC or state school.
In terms of number three, that is DEFINITELY something you can do. You take two years of junior college and get all the general education requirements done. Again a counsellor can make sure you take courses that will be accepted by the school you want to transfer in to.
So look into individual schools. I'm planning on going to a 4 year college, and over summer and maybe during normal semesters start taking courses at a junior college. It's cheaper :).