1. Yes you can
2. Yes
3. If you get your line activated in store you are charged 45 dollars. It's free online. You can get a prepaid Sim anywhere and activate online for free
4. As soon as you do it online for prepaid
5. If it has quadband 3G and at least band 4 lte plus others then it should be compatible.Koodo does also have a comparability tool to put your phones Imei into: https://www.koodomobile.com/en/help/finding-your-imei 
6. Here is the list of countries you can call on prepaid: https://www.koodomobile.com/en/help/long-distance-travel-and-roaming-prepaid

I suggest if you want to make international calls that you use calling cards or VoIP options instead.

Thank You very much @Goran . that helps a lot. I have one more question- what is tab plus/mid plan? do i need to get a device from koodo to get these plan working. are those post paid plan?

You asked about prepaid before, so the tab doesn’t apply there. You can use any compatible phone without having to worry about that :)

For postpaid plans, the Tab means that you can pick a phone with your plan, and then it is paid over the next two years instead of all at once. The bigger the tab, the less you pay up front and the more you pay per month.

@Sophia Thank you very much. Now I understand this now.