Hello Melu.
Welcome to the forum.
As for the "mental happiness" (aka brain rewiring), PM can help with taking the edge off of your GD and as you mentioned, also triggers breast development. This could be particularly useful for you since you're having difficulty with seeing a gender therapist and starting HRT.
In regards to the health issues, I wouldn't worry, assuming you're in good health overall. The one problem I had with PM is headaches caused by estrogen dominance, but it's very fixable. Here's my thread on that:
http://www.breastnexus.com/showthread.php?tid=12221
Also, here's my latest breast development with pm:
http://www.breastnexus.com/showthread.php?tid=22592
I think taking pm would be beneficial for you, both mentally and physically. You may eventually move on to strictly HRT later on in the future, but in the meantime pm can help make your GD more tolerable and get the ball rolling on breast development.
I'm not aware of any long-term risks of taking pm. Next March will be my 3rd year of taking pm, and I haven't had any such problems. (I'm 28 btw).