A lot of these factors depend on the school but I'll answer based on my university.
I was admitted to USC back in 2001 as a B.S. in Aerospace Engineering with an Emphasis on Astronautics major (rocket science!).
I cam down to the school about a month before classes started and went through orientation where I took a bunch of placement tests and went to some presentations about various stuff (loans, housing, meal plans, extracurriculars etc). Finally I visited with an advisor and based on my placement results and degree objective I planned out a first semester schedule.
Then a month later I came back, moved in and started going to classes etc.
As far as things go here, we have a course catalog that says what classes are required for a degree in something and it usually has a sample course plan for every semester. Things are of course flexible based upon AP credit, placement exams and advisor's. For example here are the current degree requirements for a BS in CSCI:
http://www.cs.usc.edu/admissions/undergrad/CSBRO.pdf These are different than what I have completed to get my B.S. CSCI thanks to transfer credit, and an super awesome advisor as well as me being on a different course catalog.
W/R/T course selection freedom, it again depends upon the school and program. CS here is pretty structured and they actually cut down the number of tech electives CS majors choose from (they added two more required classes and took away two tech electives). However tuition doesn't change if you're taking 16 units (the average 4 class load) or 18 units so a lot of times people do tricky things so they can take 5 classes in a semester.
Double majoring is pretty crazy and a lot of times people do it in overlapping fields to cut down on the number of classes. I honestly don't know how it works for different majors.
Minoring is pretty easy if its related to your major. As a CS major I probably could easily minor in EE or Math. I'm actually going to end up 1 elective short of a minor in game programming (the minor was 4 additional classes and I had to make two of my tech electives certain classes but that was no big deal).
Uh yeah hope that helps, I probably missed some of your questions if so let me know and I'll try to answer them.
Not neccesarily. Some majors require a minimum GPA.
Only if you want to get in the Major your very first semester though, right? I think you can apply for most programs after your 1st year even if you didn't get into the program straight out of high school. As far as I know, they only look at college grades if you apply into the program after you are already a college student.
Depends upon the school and program. I started taking CS classes without having my major officially changed and I probably could've taken Film School classes had I wanted. Actually switching majors to Cinema would've been a lot harder than switching to CS was though.