Judging by posts from other CDers who have told their wives, some common questions are:
Do you dress this way because you are gay or are attracted to men?
Do you want to be a woman?
How long have you been doing this?
How far do you see this going?
How often do you dress or want to dress?
Am I enough for you?
But, we don't know your wife nor have we any idea of the quality of your relationship. We cannot anticipate all her questions or concerns. So as you said, just be honest.
Also, don't minimize or downplay what you do or what you want to do. Nothing is worse for a wife than her husband telling her that he only likes to wear underwear occasionally, but then he slowly ramps it up to wigs/makeup/breast forms/hip pads/body shaving/pierced ears/growing finger nails/wanting to go out fully dressed/wanting to dress more often/wanting lots more clothes/etc/etc/etc. Ask yourself what you would like to do crossdressed in an ideal world, what clothes you would like to own or what look you would like to achieve, and be honest with your wife about this - even if you're not there yet.
EDIT
One more thing. What upset me the most was not how my SO looked while dressed compared to me, but once the floodgates opened and it seemed that my SO thought of little other than wanting to achieve a certain look, and all the purchases began to arrive at the door, I felt truly left out. I had been accustomed to being the object of desire in my prior, long-term, hetero relationship. And then all of a sudden, it seemed as if my SO's own appearance was a bigger object of desire to him than I was. When he saw pretty things in a store or online, he wanted them for himself more than he wanted to see me in them. So I competed for his attention. I bought clothes for myself that I thought he would find sexy. I tried to compete with women who were half my age (my SO was attracted to the young, beautiful woman look). This went on for years until I hit bottom with it. I realized eventually that I really had nothing to do with what or whom my SO was attracted to. And then I was happy with who I was once more.![]()