I'll weigh in on the IM vs SubQ. I do IM, use a 25g 1" and use thigh. First couple of times was super freaked out, but painless. It did leave some soreness the first 3 times, but after that no issues at all.
I would recommend on online clinic and not do it self sourcing, at least for the first year or two. Plenty of reasonable easy sources. I used Nuform, around $57 per month for the test and $179 join fee. They did provide an AI just in case, but I have not needed it. It's a game changer! I have my first blood test next week, so don't know where my test sits now, but targeting 900.
As for the holy trinity, I can attest to that. I am using Reta (5mg), HGH (2iu) and Test(160mg x split twice weekly). I have reduced by BF by 5% in 90 days using this. Put on more than 5lbs of muscle and lost 11lbs of fat. I am 52 and found that in the previous 18 months of lifting and getting adequate protein, could barely move the needle on muscle gain. Lifting heavier and recovering better. I have not seen as much improvement in sleep as I would have liked, but have seen some. I highly recommend it.