This is a good book about century (and beyond) training:

http://www.amazon.com/Complete-Book-.../dp/1579541992

The 10% rule is a good one. So is is taking a "rest" week (not required to be totally off the bike) every 3-4 weeks. It's ok to fit rest weeks in to your life, like when relatives are visiting or it's busy at work.

Don't make getting down to 220 a requirement to do the century. If you keep riding, the weight will come off.