Re: Ukemi worried
First off. Everybody here has all the best wishes for you to succeed. Having said that, don't take any specific instructions from the (i.e. how to do rolls). We are not your teacher. We do not know you physical capabilities. We do not know your emotional constraints. Every instructor has their own way to teach; every style of aikido has their own way of rolling. Take instruction from your instructor. That's his responsibility.
Secondly, I'd like to restate something Mr. Dewey said. His statement was, "The single most important thing to remember is to not take a fall unless you're comfortable with it and you have been given plenty of hands-on instruction on how to do it correctly."
You should never try to "stop taking a fall". That's a good way to get hurt. When you see a technique that requires a fall you are not comfortable with, speak with your instructor and voice your concerns.
It is your instructor's job to push you beyond your comfort zone. That is something completely different from endangerment. You're going to have to understand the difference between the two, and if you don't, again, talk to the instructor about it.
Good luck, it's an amazing ride!