For the last three years I have done about 500-550 hours, 7500-8000 miles and about 750,000 feet of climbing in a season. I spend much of the summer working on endurance paced climbing, with a lot of back to back hard days on the weekends. For example, 10k feet of climbing (at about 85-90% of FTP) on saturday and 5000 on sunday. This year I did over 20,000 feet of climbing every week for three months. It wasn't a goal, it just happened.
Most people do a lot more regular races and training, and much less training for EC than I do. I like that kind of riding so I do a lot of it. I don't think it's required to do well at EC. But if you don't put in some 20,000 foot weeks it'll probably be hard for you to finish.
You also need to work out your fueling strategy and test it well.