What do these labels, ‘transsexual’, ‘transgendered’, ‘trans-women’, ‘gender dysphoria’ & so forth, really mean?  What’s it all about?  

Gender dysphoria, the mento-emotional component of being trans, involves feelings of low self-esteem, a distorted sense of self, depression, anxiety & obsessionalism.  And it is clearly hormone sensitive. 

A transgender person is someone who happens to possess the unambiguous reproductive system of one gender, but feels that he or she belongs with the opposite gender. She doesn't choose to be transgendered, the transgender drive chooses her.

Yes, it has clearly been proven to be. 

Some forms of transsexuality are inherited via abnormalities in the power of the androgen receptor gene.

 Gender dysphoria is suite of mental symptoms experienced by transgendered patients who have been unable to feminize. It may be testosterone-driven.

Trans-genderism or transsexuality of the M to F variant does not appear to be linked in any way to sexual orientation. Having said that transsexuality is a mixed bag.