I ask bc this is my first ironman. And I have not done a 112 mile bike after an OW swim in high 40’s temp. There are definitely new factors. I am not even sure how changing works in T1 … the athlete guide just talks about your bags not the actual logistics. Lastly, shedding layers seems like a way to go but not sure if you are allowed to at the aid stations (and likely wont get them back). I get these are noob questions but just trying to make it to the finish line in one piece.
For anyone not gunning for a KQ, I offer this advice when I was faced with a similar conundrum (Tahoe 2013).
Air temp was 33 at swim exit, water temp was 62 (ish). Cold morning.
I planned a full change in T1 and T2. I had a towel, bib-shorts, regular short sleeve cycling jersey, compression undershirt, arm warmers, under-helmet beanie and a cycling jacket in my T1 bag.
Got into the change tent, and despite the ridiculous crowd in there I found a little spot, stripped completely, towel-dried until I was sure I was as water-free as I could get myself, and put on all the kit I brought. My T1 was a long 14 minutes, but it looked like that was pretty much the median time for most people that day (lots of people did what I did).
About half way through the ride the temps climbed to the mid-70s and I shed the jacket. I stuffed it up the back of my jersey (I am sure that was really aero, lol). I finished the ride still wearing my arm warmers though.
In T2 I shed all of that except the compression shirt. Put on a regular running tee, running shorts. Changed socks (fresh socks in T2 is important, at least to me). It was warm by this point so I took off the arm warmers but I tied them to my bib-number belt. I knew I would want them later when it got dark. Sure enough when the sun dipped the nice 70 degree weather turned to low 40s quickly. Put on the arm warmers and I felt great.
Now - you guys are not going to have such extreme conditions, however the advice applies. Towel off in T1, get dry, put on regular cycling kit (or dry tri kit). It will take you an extra 5 minutes in T1 but you will be more comfortable. If 5 minutes matters to you, then you probably don’t need to read this anyway 
In T2, might as well full change again. Take the extra 5 minutes to be more comfortable.