1) 2 weeks in the minimum amount of experience, but you may be 'competing' for 1 space against several other applicants. The more you have, the better advantage.
2) End of September courses will open for browsing. This is the time to find courses you like, contact references, write a personal statement and contact providers with questions. Application will open for submission about 2 weeks later (October 18th). As above, some subjects/providers are desirable and have limited spaces. first come, first serve.
3) So you'd apply this year (October 18th) in order to start next year (17/18). Apply 1/2 are just phases of applications. If you're rejected/withdraw from your initial 3 choices you need to wait until Apply 2 in January before you can apply to additional providers one at a time.
4) All courses for 17/18 will be on UCAS at the end of September. You can find part-time courses, but the majority are full-time (1 year). Most courses will grant you a PGCE (it has MA credits) but you can opt to gain just QTS (minimum teaching requirement)
5) University-led routes just mean you'll start in schools around December and spend September - December FT in University. It works more in blocks (block of uni, block of school)
School-led routes (SCITTs) mean you start in September with the kids and usually have 1 day a week to go to your provider to study. Within SCITTS are 2 independent charities (School Direct and Teach First) that offer slightly different experiences but are a lot more competitive to get onto. Read into them. Basically, it's your choice how you want to learn.
6) You A-Levels don't matter, your degree is a higher level of qualification and essentially 'overrides' them.
7) You will also need to pass numeracy and literacy skills tests before you can teach. Your offer will be conditional until you pass these. You only have 3 attempts on each - if you fail, you cannot apply to teach for 2y.
8) It's all personal choice. If you take a year out, you can apply for a paid position as a TA or Cover Supervisor, or even join a Teaching Agency. As your 'specialism' is Science, you'll be sought after. Also, you're eligible for a tax-free bursary because of your subject.
Here's a FB group for trainees wanting to teach next year
www.facebook.com/groups/TeacherTraining1718/