The standards of care are in the Wiki here, just look up WAPATH Standards of Care.
Or
www.WPATH.org and down load SOC7.
No you do not have to be full time or in RLE to be on HRT, that was phased out a long time ago.
Basically the psychiatrist or mental health professional ( who can be anyone with the training) clears you that:
You are competent to make a decision, which means you understand the consequences fully.
You do not have co-morbidities that prevent you from making a clear decision.
You do not suffer a physical ailment that would worsen on HRT, usually this is related to high blood pressure or clotting conditions. These may be worsened by smoking or obesity and the medics may not allow HRT unless these factors are under control.
You are over the age of consent for your country. If you are not there are legal matters that need to be dealt with.
After being on HRT many, but not all surgeons, want at least 12 months RLE before they will accept a psychiatrists letters for you to have surgery. If you don't want surgery that is irrelevant.
These rules do vary a little from country to country and some medics impose their own variations but that is not indicated in the SOC 7.
I would download SOC 7, read them and make sure you have the information to hand when you need it.