How to talk with my advisor about PhD project?
You're going to be stuck with your adviser and the chosen topic for several years -- so you better be honest in your conversation and say what you really think. I don't think there are any off-limit topics. The worst that may happen is that the areas you are interested in have no overlap with those your adviser has knowledge of/is interested in, and which he might decline to advise -- but that would be good to know as well.

When I have these conversations with my students, I actually do not offer any topics. I ask my students to come up with areas they are interested in, and to think about what they want to do before we make decisions about PhD topics. There is nothing worse -- for both sides -- if a student is stuck with a topic they are not interested in, and so I let my students choose what they want to do, and only steer things a bit to the left or right given my knowledge of what the relevant topics today are.