Regarding injection site, there is no superior or inferior site. It's what works best for you. Most docs are set on giving patients harpoons to inject, but that is old school. You do not need to inject deep into the muscle. Actually, several studies have shown that subcutaneous injection work just as well as IM injection, you do not need to inject into the muscle at all. I prefer shallow IM injections with a 1/2 inch 28G insulin syringe. I also prefer the quads because I pretty much where shorts year round where I live and the quads are more accessible to me without having to disrobe.
Regarding frequency, injecting smaller doses more frequently is superior than larger doses less frequency. I prefer the every 3 day protocol rather than the MWF protocol, but either is fine. With the E3D protocol. just pick what works best for you.
Regarding inject site, it doesn't make a difference. I inject into the quads, but with a smaller 5/16 inch 31 G insulin syringe. Not sure if it actually gets into the muscle, and it doesn't make any difference. Just get it into the body. As for frequency, I prefer to stick with the same schedule as my T injection. It just makes things easier to remember.
Regarding test booster, I agree with Windex, about all they do is drain you pocketbook. Save the money for the meds that matter.
Regarding AI, the term is used for "Aromatase Inhibitor", which is a class of drug that inhibits the enzyme that converts T to E. Anastrozole is the most common of the AIs. I agree with Windex that if you are using traditional TRT doses of T and are injecting on a 3X per week or E3D protocol, you should not need an AI. Guys need E too for erections and libido and AIs are extremely difficult to dose for guys. The drugs are manufactured in doses that are designed to treat breast cancer in women, who have much higher levels of E. Most guys end up crashing their E when they use and AI and end up with a bad case of ED and wonder why their TRT is not helping. Best advice is to NEVER use an AI unless you have the correct labs that indicate you need it and then to follow up those labs with careful dosing experiments. I talk about this in the "Best practices" sticky.