Century rides in good weather are not a problem if you have trained enough. Same with the bike. If it is serviced properly and has no problems on it- it should do 100 miles or longer without needing any adjustments or repairs (And I do undersatnd that parts can fail at any time)
Main thing is that you are going to be sitting on that bike for a long time. Saddle is obvious but brakes have to be reliable. Gear changes must work properly. 100 miles on trying to get the gears to change smoothly can be annoying and that change you made to saddle height last week must be proven to be correct.
Weather is the factor you cannot cater for. You have to be prepared for it and that may mean carrying a few extra coats or jerseys at the start or having a place to carry discarded heavy Goretex jackets when it dries up.
Couple of pics of my Century bikes but the main one is the Tandem. That does 100 milers witout any other problems than a bit of Butt ache after about 8 hours. Probably down to the saddles changing shape with all the rough stuff. Road rides and it is just one of two bikes. Flat ride and the Boreas gets used with its Compact crank. Hilly ones though and the TCR-C is favoured as it now has a triple fitted.