Sounds like you are going to use the outside method of applying, suggesting your spouse is still living in Afghanistan...
1) The application package (including your sponsor forms) are sent to the Case Processing Center in Mississauga, Ontario. From there, it will be approximately one month for you to be approved as a sponsor. After that stage is completed, the application is then forwarded to the overseas visa office assigned to handle cases where the spouse lives in Afghanistan, which is in Islamabad, Pakistan.
2) My wife's case was processed in London, England, so I can't help you here.
3) There are lots of things you can use. In the case of my wife and I, we used photos from the different trips we took to visit each other, copies of emails we sent each other, copies of MSN logs of chats we've had with each other online, copies of long distance records showing how often we speak to each other, letters from friends and family testifying to seeing my wife and I in person, spending time together, and stating we are in a true relationship, we even had a letter from my church pastor stating that he did online pre-marriage counseling with us. Other things you can include are receipts from gifts given to each other, copies of cards and letters sent to each other, copies of money transfers sent to each other, stuff like that.
4) Like you hinted, you are exempt from financial requirements as this is a spousal application. However, you must not be receiving social assistance from the government, nor legally bankrupt. Student loans or line of credits are NOT considered social assistance.
5) The medical exam technically isn't required to be included in the original application. If you don't include it, the visa office will just contact you asking for it. However, doing it this way only delays your application being finalized. My suggestion is to have your spouse do her medical as close to the date that you send in the application as possible. Doing it in advance saves time, which is obviously beneficial to you and your spouse. Keep in mind the medical expires after a period of time, so you don't want to do it far in advance.
Use this link to find the closest DMP (designated medical practitioner) for you. One thing I do know is that there are no DMPs in Afghanistan, and you have to get the exam by a DMP, not just any doctor.
http://www.cic.gc.ca/dmp-md/medical.aspxAs for tips on how to get through this. Keep on posting questions about the process. We've all been through it, or are going through it. The more we share, the more we help each other out.
Also, download the application package and guides. They are quite user friendly, and answer a lot of questions for you.
http://www.cic.gc.ca/english/immigrate/sponsor/spouse-apply-how.asp#step1