Yes, you can sponsor your wife while you are away at school. I am working abroad myself, and know the procedure quite well.
When you apply for your sponsorship, it is important that you indicate when you will be returning to Canada, and how you plan on supporting yourselves (job, family, etc.) when you do return. Amount of income is not important for Family Class, but you do need to convince them you will move back to Canada when your wife gets her PR approval.
As for visiting during school breaks, you will need to apply for a TRV (if not visa exempt) for your wife. This will be difficult for most as they are often refused, but it is not impossible if you do a convincing application.