I can talk about your question on serotonin and dopamine (not so much testosterone).

Serotonin and dopamine are not "happy chemicals". That is a very common misunderstanding and a huge oversimplification. They are neurotransmitters with an enormous number of roles in the body, some of which are indirectly related to regulation of moods and emotions and most of which are not. But they do not, in and of themselves, cause "happiness" or feelings of reward. They're a means by which neurons communicate with eachother but they don't themselves carry information about what the message being communicated should be. Their actions are highly context dependent and depend on myriad other influences (neuroanatomical context, receptor type, modulating influence of other neurotransmitters...it's extremely complex). Trying to understand mood by looking at a neurotransmitter is a bit like trying to understand how a car works by studying the chemistry of the materials it is made from.

I kind of think of neurotransmitters sort of like sending messages in a large office. There might be several ways you can do that (email, written note, formal letter, telephone, face to face). Each method being analogous to a different neurotransmitter. Different methods may be more or less appropriate for different kinds of message but knowing the means of communication tells you nothing about the message itself. This is (very much simplified) the mistake people are making when they talk about serotonin and dopamine being "happy chemicals" and quote scientifically illiterate ideas like "dopamine hit".

We don't actually know how SSRI's work either. A lot of the "serotonin is a happy chemical" stuff actually comes from the observation that SSRIs do work, not the other way around. "SSRIs work therefore serotonin must improve mood". But there is growing evidence that their mechanism of action WRT depression may not be anything to do with serotonin at all. At least not directly. I mean they definitely do inhibit reuptake of serotonin but that is not necessarily how they are having their effect on mood.

This 2022 paper gives a good overview of where we're at with that stuff: https://www.nature.com/articles/s41380-022-01661-0

>The main areas of serotonin research provide no consistent evidence of there being an association between serotonin and depression, and no support for the hypothesis that depression is caused by lowered serotonin activity or concentrations.