I would aim for 8 reps today, 10 next session and 12 the last session if you can. Remember it is the weeks work you are trying to get through, not an individual session. You will probably think today is a bit light, but keep the intensity up and it will still be a good workout. Also remember in the first week you are also trying to get an angle on what weights you will be wanting to use once you have settled in to the program. You will only really know that though at the end of the 3 sessions, you wil know then what needs to be upped and what you can keep as is.
I found that I started with bench at 50% thinking i would easily up it in the second week, but i couldnt get all 12 reps for three sets in the third session, the effect of shoulders before it has just killed it. Also remember there is 5 sets of dips that will smash the chest too. There is no need to overdo it on bench (or any other single movement tbh), cos then the dips will be affected and it the WHOLE workout you are trying to do in balance, not just one particular part of it. it all fits together really well and every move compliments and effects another...
You're gonna love it buddy