I'm not a century or training expert but here are a few thoughts/questions. I'm a big fan of spending some time off the bike, for no other reason than I think it provides a mental and physical balance. Yoga is my drug of choice in that regard. It has the added benefit of counterbalancing some of the effects of long hours in the saddle and strengthening my core. Pilate would likely have similar affects without all the "oms." If I were you, I would try to include it in my routine.
I, personally, haven't been doing any lower body lifting since I got back on my bike in March. But that's more because I don't love it and reserve it for fall/winter. I've been doing some slight upper body lifting at home to keep my arms toned, but it's just with light weights. I do recognize, however, that lower body helped me strengthen my glutes and hamstrings and that I feel stronger on the bike in that regard I've seen some added strength on the bike this year. If you do keep lifting, I would stick with higher reps and lower weights to (hopefully) guard against injury.
My concern, however, is that riding six days a week and doing Pilates and lifting doesn't give you much of a rest. In my opinion, planned rest days, over and above either lifting or pilates, will better prepare you for your first century. My suggestion would be to ride 4-5 days a week, do pilates and/or lift on one of your off days and take a day off from all of it the other. That suggestion is based, however, on the assumption that you're still able to get some good miles in in 4-5 days time.
Also, keep in mind that you don't necessarily have to follow the same routine each week. I, too, was preparing for my first century (completed it last weekend at the Horsey Hundred in Kentucky). Depending on the week and the weather, I might ride an extra day and skip my usual yoga class or ride one less day and go to an extra yoga class. As long as I was getting my miles in (at least 150/week) with some hill work, I didn't stick to a strict routine. I will tell you, too, that the one week in which I rode 6 days, I hit a wall and had to take a an unplanned day off. While that day did me a world of good, it made me acutely aware that my body has its limits.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher