Neither was painful to me. I was mildly sore for the first few days after top surgery, but that went away very quickly. I had no pain or soreness whatsoever from my hysterectomy. I had top surgery at 25 and a hysterectomy at 26, phalloplasty will be this year at 27.
I don't think there is a "best" age to get either. It's all about when you're ready for them and you've done enough research to know what's right for you. I got top surgery first because I had been binding for several years and was tired of it. I had my hysterectomy when I did because I wanted to schedule my phalloplasty and I had to have a hysterectomy three months in advance of that.
One thing you should keep in mind is if you are having insurance cover these procedures, they may want you to do things a certain way and in a certain order. It is best to ask them what their requirements and procedures are for gender-related surgeries if you're planning to have them foot the majority of the bill.
With any surgical procedure, there is a risk of nausea and vomiting. It all depends how you react to the anesthesia. If you've had any kind of surgery before, that would be a good indicator of how you'll respond. I was very nauseous after top surgery and needed an extra dose of anti-nausea medication to feel good enough to get up and go home. I had no nausea after my hysterectomy, but I had mentioned to the anesthesiologist that I was prone to nausea and she said she would take care of it.