Hardest part for me has been keeping up with my deception, with telling my gender therapists that I was okay and had no severe mental health issues when I actually did, out of fear of being denied to transition medically. Not because I felt bad over lying, but because it was hard to keep track of what I had been honest about and what was lies and making it sound believable. I don't regret having taken that route, but it's definitely been very hard on me. But oh boy, do I look forward to after my SRS hopefully daring to open up about those issues I've kept hidden for more than the past decade now. Only a year or two left, shouldn't be too difficult to power through now. I've been very worried about the therapists possibly denying me further transitioning if they'd know those things about me, and I just never dared to take that risk after I've done some research online about it that further proved my concerns, although it's been very difficult to find the answers I've been looking for and I'm still not sure. It's too rare. But I hope that when the only thing transition-wise I'll have to worry about is keep getting my testosterone shots, I might dare to take that risk.
The thing is that I knew I could not continue living without transitioning at the point I came out as trans, so trying to treat the other issues first just wasn't a possibility. I also knew myself well enough to know those issues are separate from me being trans but that no therapist would just take my word for it. Basically, I knew I needed transition first, then deal with the trauma-aftermaths, not the other way around. But the system doesn't work that way. Had I been open about it they would have (very likely) refused to let me transition before having dealt with the other stuff first which would (also likely) have postponed my transition by at least several years which I wouldn't have been able to do cause of my dysphoria. It was a "catch 22" that went on for years and constantly kept messing with me, that I had to be mentally stable to transition but I couldn't be mentally stable without transitioning. This was by far the greatest hurdle ever in my life, transition related or otherwise, because it felt so hopeless and never-ending with no exits or solutions available. I've no idea how but eventually I guess the gender therapists started believing my lies and deemed me "stable enough" and from there on it has been going in the right direction for me. This was my decision but I DON'T recommend anyone else doing something similar. It's soul-wrecking with a high risk of backfiring on you. But I'm a stubborn idiot, I guess. It changed me, for better but mostly for worse.
Otherwise, the waiting itself and the uncertainty of not knowing if I could ever get to start hrt or not, weighing whether or not it was worth it to self-medicate with hrt or not, totally wore me out in the beginning of my transition as well. And also that I had way too high expectations of testosterone once I did get to start taking it definitely was a struggle for me too, when it didn't meet those expectations. Facing the reality that the physical aspect I've always been the most dysphoric about I might not be able to change at all, most certainly hasn't (and still isn't) easy for me to deal with.
With that said, my struggles with passing, accepting myself after or during my denial and even learning to stop sweaping my important issues under the rug cause they "don't feel that bad and I'm probably just overreacting" have been easy in comparison for me.