Many Questions Regarding iPhone

Hi, I am a newbie when it comes to iPhones. My iPod Touch 2G recently broke (and I don't have a phone atm) so now I was thinking about upgrading to an iPhone 4. So to break it down into questions to make it easier for those who may lend a help.

- I will be jailbreaking + carrier unlocking -

1. What is Activation? Is it something I/everyone has to do? If not, should
I?

2. Any risks when -jailbreaking-, -unlocking-, or even -activating- with the iPhone? I heard about things like bricked (but that is not my concern) but are there additional risks that only the iPhone (Not iPod Touch) has when jailbreaking, etc?

3. iPhones in Canda don't require us to stick to AT&T (Like in the US) and we are able to choose + switch our carriers freely whenever (ie. Rogers, Fido, Bell and Telus). I am aware that we can buy iPhones w/ or w/o contracts. But is it possible to go with a plan (ie. Fido) and use that plan internationally in Korea without ending up with a fat phone bill?

4. If #3 is not possible, what if I buy a 2 (or so) year contract with Rogers, and then unlock my phone (jailbreak), use a SIM card that works in Korea and then when I come back to Canada, and continue to use my Rogers contract? Of course during the time in Korea, I will hopefully not end up with a fat phone bill from Rogers...~ Basically I'm hoping that I'm not paying anything for Rogers (or anything that's unnecessary) while my 5 month stay in Korea.

5. You can buy an iPhone 4 at the no commitment pricing but they will require an iPhone activation to purchase it. You can cancel the plan after you walk out the door. <- What's that mean? Will it benefit my situation?

Sorry if my questions are a little unclear. Please let me know so I can further clarify for you. And sorry if there's been a post like this one, as it is really hard to search and find all the questions I needed answered. And I'm sure other iPhone newbies like me that are in the same situation would be glad to have found this thread :)