My thoughts on your questions:
Do you think the majority of people are gender critical, and why/why not?
No. Sadly many cultures are still deeply repressive especially of women's freedoms and right to self-determination and equality with men in practice if not in law. But globally, all cultures, even the most sexually equal ones, still have some degree of socially expected and enforced gender roles, and usually more to the detriment of women than men. Why? Because we learn what's "normal" within our culture from the day we are born. It takes an effort of will, and usually someone asking us hard questions, to actually see the everyday social structures around us and realise they are contructed rather than just "the way things are". And even if you do see that, it's still a huge effort to stand against your culture, likely your friends and family, to change them. It's like opening a box with a crowbar when you and the crowbar are both locked inside the box. So most people to some degree do accept and live within the gender roles of their society.
Globally, the right wing is more vocally gender critical than the left. They are also far more likely to be regressive on a range of women’s issues like abortion and anti-gay. Why do you think they agree with GCs on this one issue but disagree on so much else (if you think they do?)
I'm not sure what you mean by "right wing" given that this phrase encompasses everything from Facism to liberal economies favouring private ownership to conservative religions. Indeed people who are right wing by one definition are often a perceived enemy of the right wing by another definition. It's almost like the label itself is ridiculously simplistic and used to turn complex realities into shallow soundbites.
Assuming from the rest of your post your concept of "right wing" is the current populist meaning of socially-conservative-to-the-point-of-repression, I disagree that this group is at all gender critical. In fact they are highly supportive of gendered roles although unlike genderists they do not support cross-sex adoption of these gender roles. This is in contrast to gender critical people who do not support gendered roles at all regardless of whether the role is being performed by its traditional sex or the opposite sex. The only time its acceptable to perform gender in a gender critical sense is when it is done knowingly, to show up the construct. This is why gender critical people celebrate men enjoiying dresses and makeup yet are critical of trans women in sterotypically female presentation - it's because the first undermines steroetypes of womanhood while the second embraces them. So, given your framing statement the right wing is more vocally gender critical than the left. is wrong, the rest of the question is meaningless.
How many trans people do you estimate there are globally?
This depends too much on how you define "trans people" to answer - you'll need to be more clear. Is it simply anyone who currently claims a transgender identity for any period of time regardless of how long that has been for? Do you include people from non-Western cultures who have different gender constructs who may not consider themselves transgender in the Western sense? Do you mean people who have taken significant surgical and/or legal steps to permanently adopt a cross-sex persona? Would you include gender nonconforming people who woudl not define themselves as transgender? This one really does need you to put some skin in the game first.
Looking forward to your thoughts on my replies @ChirpyFinch