Hi Beth, welcome to Susan's!
I am the SO of a MTF, and I have found Susan's to be especially helpful, and I can only hope it does the same for you. Everyone here is quite intelligent, open, and supportive. I think you will find that the unique thoughts and experiences of others here sometimes make it easier to accept and understand the things that are happening in your own life.
Now, I agree with you, and I am sure many others will as well, that it is important for you to talk to your wife as soon as you can comfortably breach the topic. I am sure it is difficult for you to articulate quite how you are feeling to her, but I hope that the two of you can talk and work through things together. There are plenty of individuals here who have married and then come out, some of the individuals have discovered that their partners are supportive, and others aren't quite so lucky, but you won't know until you try. I am sure that some others will be around to give their two cents, and their advice there is probably a bit more sound than mine (my SO and I aren't married, and they can probably give you some pointers on how to best organize your approach to this sensitive subject).
Now, the one thing you didn't clarify is are you MTF, or do you identify as a crossdresser only? There are plenty of people here who identify either way, but it changes things a bit depending which you identify as (in terms of coming out to your wife/where you ultimately hope to be in life, i.e. transition, etc).
Also, to try and calm your fears of height a bit, I am a genetic female, and I am 5'9". I have a handful of cis female friends who are 6'+ and no one questions their sex. There are also a few ladies on the site that are quite tall, and let me tell you, they are gorgeous! Being tall isn't the be all end all, many people associate tall women with models. The key is to be confident!
I hope to see you around the boards. Welcome again, Beth!
Hugs,
Jacquelyn