You can apply to extend your visit visa based on that you want to explore Canada, spend more time with your sister or whatever you want. There is no guarantee it will be approved though. You will have to prove that you can support yourself and that you will leave at the end of your visa.
To get a student visa, you would have to be accepted to a university, you would still have to show that you can support yourself and pay your tuition and that you will go home a the end of your visa. If you have already applied for PR via FSW, it may be hard to prove you are going home at the end of your visa. You can apply to change your status from visitor to student.
To apply as an FSW under category 1, the list of 38, you only need 1 year experience in the last 10 years in one of the occupations on the list and you need to have at least 67 points. You need to have letters from your former employers. If you can't get a letter from your former employer, the best you can do is write a letter yourself about your job at that time and your job duties and get a former co-worker to verify that you worked there and did that job and hope that is good enough.
You will need a new police clearance when you are asked for documents and as for the IELTS, it's better to take it before you apply because then you can be sure of your points before you apply but if you choose to guess your points and take IELTS later when you are asked for documents, you can do that too.
It's up to you what country you apply from. If you have at least a one year visa in the UAE, you can apply there. You can have the medical exam in Canada if you want. You can look at processing times at trackitt.com/canada-immigration-trackers/federal-skilled-workers
You can find answers to many of your by reading your application guide at
http://www.cic.gc.ca/english/pdf/kits/guides/EG7.pdf and you can find a lot of other info by browsing through all the skilled worker pages starting at
http://www.cic.gc.ca/english/immigrate/skilled/index.aspHave fun
