First let me say thank you for comments about the website, as for buying a Honda, excellent product, but Honda also come with an inflated high price tag. and in my mind today you can buy equal quality for less. you want to buy the label you pay the price.
As for your # 2 question, I don't think you read the web page " paying cash " what's your best price "
Your # 3 question - Buying private is more risky than from a dealer, navigate to this web page http://www.usedcartips.org/DMV.html and click on Quebec, the way I understand it - the seller cannot sell you a vehicle with a lien in place.
# 4 " Negotiation room " a good question " go autotrader.ca enter you postal code, and enter the car in question, am sure you will find many within 100km,,, from there it comes down to how much you have studied to learn the process how to buy a car.
As much as I appreciate your comments, I am sorry to say your whole post about questions where detailed in the this website, but don't feel bad 75% in this fast living pace don't have the time to study with more important matters at hand than buying a car.