I give this advice to a lot of guys. Obviously go read up on the signs of high and low estrogen in men.
You should notice if you tank your estrogen. You will be tired, no libido, dry creaky joints that hurt. If you notice anything like that the day after you take arimidex then wait three or so days with no arimidex dosage then start again at a lower dose. It might even start two days after you dose arimidex, everyone is different.
Really since you are going for your first cycle, you are taking HCG, and you will have both arimidex and Nolvadex on hand, maybe start off without any arimidex or Nolvadex. It is so easy to over use arimidex. Since we need the estrogen to build muscle and so many guys seem to never have issues while never taking arimidex then why not safely find out if you even need arimidex on cycle. You are not taking a crazy dosage of test so you are well within the window most guys seem to tolerate.
This is just an idea for how you can find out if you need arimidex at your given dosage. Start out without anything ancillaries, no arimidex no Nolvadex. If you get puffy nipples or anything that seems like gyno then take Nolvadex at around 10mgs every other day to every day. That should address the gyno. Now if you do end up needing the Nolvadex and you start showing other signs of high estrogen like bloating, high blood pressure, emotional roller coasters, and or no libido then dose the arimidex at 0.25 mgs on days you pin.
One way that I myself notice the estrogen issues is in regards to morning wood. If I am running a cycle and I notice a drop in libido that could be just being tired or other stuff but if I am not waking up pretty consistently with morning wood I know the estrogen is too high. I dose my AI at night and man that next morning it’s like my dick wants to pop. Now if the morning wood isn’t there the next day that tends to mean I need to increase my dosage. Basically when my estrogen is too high and I knock it down the morning wood comes the next day but that is just because I got the estrogen lower, not necessarily to the optimal window where my body likes it. When I have consistent morning wood I know I am in the window my body likes.
You are just going to have to watch everything and then adjust accordingly.
I wish I could give you an easy to follow X dosage of test needs Y dosage of arimidex but everyone is so damn different. Then we have to deal with UGLs not making everything perfectly dosed.
With you being on your first cycle I think Nolvadex to address the gyno then arimidex lightly dosed for the other signs of estrogen would be the safer way for you to ease into this.
If you notice the other signs while taking nothing basically signs of high estrogen besides gyno then just start with the arimidex at a light dose and adjust.
Hopefully someone else will chime in with some good input for you to use.