@und3rd06 removing the collar will definitely help cool you down, it will give the body heat a better chance of venting out.
The biggest reason for the bulkiness you are feeling is the wider shoulder floaters you ordered. No amount of breaking in is going to stop those from impeding being able to put your arms in front of you. With the width of those, you could probably remove that white floater piece directly above the elbow floaters. I can see that being redundant and factoring in the bulkiness.
Were it me, I would remove the collar and trim the shoulder floaters back to the about where that white stripe is... similar to my pic of my JB553 a couple of posts up.