Help! Student questions

So this whole process is so very confusing.
I apologize in advance for this long post.

Background:

I'm in my final year of highschool, and it's about to be "choosing a college/university" time

I plan on graduating with a solid 3.0 (not too great I know). I already have one AP test done, having scored a 4 on English Lang. This senior year I plan on doing AP psych , AP Government, AP Economics, And AP English Literature.  But usually test results don't come in until June-July. And I have my SAT results but plan on retaking in October.

Current Situation:

I'd love to study over in the UK right from the get go. The course of study I'd like to Pursue is Medicine.

The Universities I'd like to go to are :
University of Sheffield
University of Nottingham.

 I'm leaning heavily on the First choice.

Questions:

With my GPA and Current classes that ill be taking, is that enough some requirements?

Can someone walk me through the Student Visa application process?

When should I apply and dates I should watch out for?

Any other information I Should consider?

Thanks in advance for your help
And sorry if I don't make too much sense ~

First question: are you comfortable with the tuition costs for an overseas student? The tuition for a medical student starts at £16,640 per year and then goes up to £30,080 (!!) for the final three years.  Remember that does not cover living costs.

You'll have to contact individual unis directly for their requirements, but I would imagine that with no biology, chemistry, or mathematics classes, you'll have a hard time getting into a medical programme. 

You'll have to contact individual unis directly for their requirements, but I would imagine that with no biology, chemistry, or mathematics classes, you'll have a hard time getting into a medical programme. 

Yes, in order to get into a medical degree in the UK, you usually need A levels in Chemistry and at least one other science (Biology, Physics, Maths or Psychology)  although, usually people apply with at least 3 sciences - a common combination is Chemistry, Biology, Physics and Maths... and usually you need to have straight As to be accepted... so for a US student, that would mean high AP grades or college level classes in those subjects.

I'm British and I took A levels in Physics, Maths and Geography (I got AAB grades - B in Maths), but I would not have been allowed to apply to study medicine with just those subjects because I didn't take Chemistry.

It can be difficult to get into a medical programme, purely because of the number of applicant - I see on the Sheffield Uni website that for 2013, they received over 3,000 applications for less than 250 places on the medicine degree - so there is often stiff competition for places.