Heya Catrin, love the attitude 
I had a similar question involving a brevet the first year I started road biking. For various reasons I didn't do it then and haven't done it yet, mostly because I realized that even the training I was doing at the time was taking a bit too much time away from my family. I wish I could get up early and do long long rides in the early morning, but fact is I need a lot of sleep too, especially when training a lot, and without it everything deteriorates including my mood and temper. So I'm headed for the long slow approach instead. That brevet of mine is not going anywhere and I'll do it someday :-)
I did have a similar project last year to tackle a long climb (rock climbing), much longer than I'd ever done before. I learnt a whole lot of stuff from it, mostly what a total wimp I turn into when I've been awake for 24 hours... and to bring that over to bike riding, I'd say:
- do do the metrics and the centuries first. Don't skip them because you don't have the time, or they're too uncomfortable, or whatever, they're invaluable learning opportunities.
- don't overestimate the physical challenge, and don't underestimate the mental challenge.
- analyze every long ride to see where your weak points are and where your strong points are, and adjust accordingly. That slight irritation you notice on a metric could wreck your brevet completely.
- pay attention to your tolerance to the weather.
And don't kill yourself to reach that one goal. It would be really cool to do it in your first year of riding, but not if it costs you an injury. It'll still be there next year.
And maybe at some point I'll even go take my own advice, and do my own brevet!
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett