I had a triple CABG (Conorary Artery By-pass Graft!) 8 years ago. my blockages were 95%, 85% and 70% if I remember correctly. You will not be allowed to drive for 6 weeks after the operation.
The post op exercise classes are essential to get back your fitness - you may even begin to enjoy them! They will probably take a vein from your leg and use that as the "tube" for the by-pass. It is considered a routine operation, but not to the person who is having it!
As Stephen said above, the main pain you get is from coughing - that is why they give you a rolled towel to hold against your chest. You will feel quite weak for at least 2 weeks.
Please DO NOT attempt any form of exercise until you are told to. I got bored and decided to polish the car roof after 3 weeks - oh did I suffer!
Be a patient patient and your recovery will be quicker! Try not to worry unduly and if they offer you an earlier appointment take it!
Keep us informed how it goes please - all the best!