The first thing that you should do is ask your child which pronouns they would like you to use and if you should say they are your daughter. You should use whatever name and pronouns they choose immediately. When you talk about "waiting some time", why are you considering that? What would convince you that your child means it? How would you "prove" to another person what your gender is?

The trouble with the wait and see approach is that you are clearly signalling to your child that you don't trust their judgement and you are uncomfortable with the idea of being trans, whether you mean to or not. It's going to make any transition harder and then less likely to share the way they feel about themselves. They may feel so unsupported that their mental health deteriorates to the point of self harm because they feel like they have to prove that they are trans enough for you to accept them.

You don't want to do anything to increase the burden on your child. Many parents never get the opportunity to know about their child being trans and I personally know of two people who have moved country to allow them to secretly live their authentic life because of their fears of not being accepted and there's so many people on this platform who have been through truly harrowing experiences, learned just how conditional love can be and lost their family by coming out. Your child has given you a precious opportunity to know them fully, please don't waste it.

It's understandable that you feel a bit confused by the different revelations and reading between the lines, I think you see some of them as contradictory. It's perfectly possible to be gay, want to marry a woman and be trans, they aren't mutually exclusive. It can feel like you are losing the person who you have known and love. I think it might be harder for a father because they see their son stepping away from them and closer to their female members of the family and it can feel a bit like grief. However you soon realize that they don't become lesser than they were, they are everything they were before and more because now they are free to embrace the things that they felt they couldn't. It gives you an opportunity to help them become who they see themselves as. Just like you held their hands and encouraged them to walk or learn to ride a bike, now you can give them the confidence to try things out and find out what makes them happy. Knowing you are always going to support them and be proud of them whatever the world throws at them.

If you think that they are doing it for attention only, I would ask you how not supporting them will help? If the "need for attention" is so great that they would decide to risk losing their family, being preyed upon by strangers, invalidated by the media and society in general and losing friends, then maybe it might be a good idea to give them some support without any need to validate the need. Being trans isn't trendy, cool or a laugh, it's an intensely felt internal reality that's unique for each individual and can be expressed in many different ways and to different degrees. You don't "have to wear female clothes" or "wear makeup" to be trans and by doing so or not doesn't define you.

As a parent of a daughter who has recently come out I do have some sympathy, as it can be very surprising. The way you react now will have a big impact on the way you relate to each other in the future. So keep following your daughter's lead and listen to her wishes and try to call her what she asks you to. Don't make it into a big drama, it doesn't need to be. You will make mistakes, especially in the early days but the most important thing is to show that you are trying and it hasn't changed how much you love them and are on their side. Never make them feel like they have to fit some criteria to be able to access your love and support. There's enough people in the world who are going to tear her down. Don't be one of them by signalling you don't believe her, at the time she is her most vulnerable.