This is the worst suggestion can be given to him. Low cardio is not at all detrimental on any aspect, he don’t have to run a marathon, but can just stick to the minumal 20 minutes sessions without worrying about losing anything from it, more than ever on trt. Aerobic training has a very huge impact on health and brain chemistry and by stimulating neuroplasticity it elevate exponentially whatever form of therapy he try (self-therapy like meditation or psychotherapy).
And you practically suggested of dying in the lifting room such that this has to become a priority. No! Again, low cardio is perfectly compatible with lifting, even with heavy lifting for maximal strength, but lifting should not become an obsession just to distract himself on another objective. I explicitly say that both form of training should be kept balanced and cardio should be kept low to not interfere with whatever he choose to do in the weight room. This is just to adhere to what all researches says about mood. He need to develop healthy, balanced routines and lifestyle.
About coffee, again, his priority should be health, and high caffeine intake is not healthy and can interfere with sleep. If he needs catecholamines (and we really don’t know), he should increase them with other methods, keeping in mind that catecholamines management should be careful and can be readily traduced to tolerance, side effects and withdrawal symptoms, if not managed well.
Even if there could been some mixed results, there are extensive suggestions that testosterone generally decrease serotonin, and serotonin and testosterone has opposite effects. I always suggest to have a medical specialist for confrontation, but about drugs that affect serotonin I have a vision drastically different from usual medical practice (although in the last years, medical community is becoming more aware of his mistakes).

