If you have problems with cold, wear the neoprene cap at least. It makes a big difference. I'm not sure about the booties, I haven't had to wear mine in the water yet, though I have them just in case. Maybe you could use a rash guard under your wetsuit? I'm not sure how easy it'd be to put your wetsuit on over full length sleeves, but that would add some insulating value.
There were definitely a lot of people pulled out of the water a couple years ago at IMCdA when it was around 56 or whatever it was. I wore my neoprene cap then. Last year the water was more like 60, and I didn't need it. I don't like it because it insulates my ears so I can't hear what's going on around me, and I have a "thing" about my ears (probably from repeat continual ear infections as a kid). Though, a guy I work with had to sit in a hot tub in T1 after last year's swim he was so cold. Some people just don't dig the cold water!
It's an excellent idea to get in the water ahead of time and see what your tolerance is. I probably wouldn't have got the neoprene cap had I not done so, and I think it made a big comfort difference.
How long is your swim?