I doubt you need any arimidex at all for 300mgs a week of test. If you were a super fat kid during puberty and still had some body fat issues then maybe. Body fat itself does aromatize testosterone, so the bigger your bitch tits get, the bigger they get.
I know I had body fat issues in puberty and for a while afterwards. I have been working against body fat since I started in the gym at 18. I personally probably could have gotten away without any AI during my first few cycles of 400mgs per week of test but I did use arimidex out of fear. I probably over used it. Really with you body fat and only using 300mgs I just don’t see you needing it. Now if something does start to happen later in the cycle then maybe 0.25 mgs on days you inject the test would be a starting dose but really that is even high. If you could make a reliable dose of 0.125 mgs I would start there but only if there was a reason to, like bloating and ridiculous water retention with gyno starting.
As far as caber and the prolactin/progesterone activity. Unfortunately you don’t know how you will react until you just use the tren and find out. Now the b6 is good to have, it is one of the few supplements/minerals/vitamins that actually do provide tangible quantifiable results in controlled studies. Now if you do have some issue, you are on tren ace and all you have to do is stop using it and within a day or so your levels will be down. Then another day or so the side effect should stop getting worse and another day or so then it should start to disappear.
I think you have a good dose set out. I don’t know your complete cycle/compound history so I can not say if using tren now is the best choice. I will say 24 is young for AAS and tren should be the last one anyone tries. I will also say I know that no one listens to words written on the internet written by someone who claims to have the experience. So just be safe and continue to at least seem to act from a position of self education.