Originally Posted by Portis
I can't tell you how hard you will find a century because that is an individual thing. I also can't tell you for sure how you will fare with going clipless. But I can tell you that clipless will help you a lot on a century. Especially on climbs, etc.
Honestly, riding a supported century, with your riding sounds very do-able to me. I'd get the clipless yesterday so you are accustomed to them by the big day.
This is an excellent point. Whatever you plan to use/wear get it now! whether shorts, bar tape, socks, or whatever... get them now. Don't try anything new on the day of the event or immediately before.
Start experimenting with foods to see what you handle best on a long ride also.