Good question, Di.
Like others, in my virtually 76 years I have to say the biggest challenge has been self acceptance. I had no problem with that until I got caught playing with my mother's clothes and makeup when I was about 8. As a result of the reprimand (this was the first half of the 1950's) I not only went into the closet but into denial. Sixty years of it! That stance had a huge effect on my life's course. But once I surrendered and accepted that I was right in the first place true acceptance by others has been the challenge.
Tolerance is fairly easy to come by, but accepting me as being a type of transgender person is really hard for some. So many people, especially those more or less my age and older who just can't get to the point where they truly recognize that such an identity can exist. They are still locked into a gender binary concept and have a hard time accepting that this concept might be in error and in fact there can be people who naturally have a goodly amount of the "opposite" gender traits and characteristics that influence their behavior and sense of self in ways that don't fit the ideology. It is not really opposite in the way all of this works in the brain, but in terms of the gender binary concept it is easy to think of opposites. It appears there are just traits and characteristics and how they are blended in each person is unique to them. I think the old thinking is changing, but thousands of years of thinking that way will take a very long time to shift.