There are plenty of training programs designed to get you up to 100 miles in 10 weeks, so 60 miles in 12 will be no problem for you, I'm sure.

On your long rides, you should make sure to watch your nutrition and hydration levels, as well as your electrolytes. For any rides longer than 2 hours, I always make sure to bring some e'lyte replacements, either NUUN tablets for my bottles or Hammer Endurolyte capsules. (1 NUUN/hr or 3 Endurolyte caps/hr for me works well.)
Hydration is important; your muscles will get sore if you're not keeping well hydrated. I aim for 3/4 of a large bottle per hour on an average. More if it's hot, less if I'm slacking and not sweating so much.
Food intake will also stave off soreness. 200 - 250 calories per hour is the standard goal when going for long distances. That's 1 Clif Bar, or 2 gels, or a banana and some Gatorade-ish drink. Nibble, don't snarf. Eat a bite every 15 - 20 minutes to keep a constant food supply going in.
Post ride, keep your hydration up for another 2 hours after the ride and work on stretching. Don't let yourself get tightened up by getting cold.

As for tapering, I don't believe in it if you're not racing. For a race, sure; conserve some energy. For a social ride, there's no reason you can't ride like usual right up to the day before your event. (I did a ride series this spring with 3 consecutive weekends: 200k, 200k, 300k. This fall, I'll do a 200k, 300k, 400k and 600k in a 6 week span.)

Once your body is used to the distance, and you know how to keep hydrated and well fed, you can pretty much just keep on riding as much as you want. Tourists routinely do consecutive 75 mile days. Randonneurs ride up to 750 miles in under 4 days. Once that training base is there, it's a matter of proper fueling.