I'm 62 now and started transition at 60. Transition rekindled my life and opened the door to the person I am today. I had a rough start and still have some bad days, but you could lay bars of gold at my feet to stop me and I'd still continue. So, don't worry you'll also find stress and hard times along the way, but you'll also find extreme joy in a gradual change into the woman you've always felt was just a remote possibility.
Yes, you may loose a lot of relationships, and on the other hand you may not. There's no way to tell how people will react until you tell them. But each person will make their own decisions about how to deal with your new life, and you have no control over them. So expect to loose relationships, and hope that it doesn't happen.
As for weight, I lost most of my weight after starting HRT But it wasn't as easy and a lot of the food I liked was off the menu. I've also lost so much muscle mass that it's now difficult to do enough heavy work or exercise in the winter to loose any weight. But getting that excess fat off my body was a must, and it meant I'd do anything to get rid of it. You'll do well if you have motivation, and I found the best motivation is having a vision of yourself and making that vision real.
Yes, doing this at an older age is more difficult in many ways, but it has made some things far more simple. I've done most everything in life that was on my list, and now I get to spend more time on my transition. My retirement is secure, while my needs are addressed and set. Yes, this transition started 40 years late, but I can't turn back time, and even at 62 I wouldn't have it any differently. But most importantly two years ago I couldn't have waited another month, week, or day to start HRT. And I'm glad I got to that point in life where I had no other option, because I can't imagine not being me.