They are quite different. The only similarity is that it's about an imagined wedding. "If you were to have a wedding..." means "if you were planning to have a wedding..." So you're asking about the preparations and not the actual day. "If you had a wedding..." is asking about the actual day. The second part should read, "what type of wedding would it be?" Using "do you envision yourself in" is awkward because you are moving from unreality to reality, and repeating the fact that it's an imagined situation. You'll find the phrase "do you envision yourself" used when talking about a very real future. I'd use "if you were to have a wedding..." because most weddings do need a certain degree of preparation. "If you had a wedding" sounds sudden.

I agree with Peachey. Also, if you really want to use "envision yourself", you need to use "having" instead of "in". Here are how I would phrase both of these questions, since they should both be in the conditional form. If you were to have a wedding one day, what type of wedding would you envision yourself having? If you had a wedding one day, what type of wedding would you have?

There is no difference Because they have one meaning

In informal speech they are the same, the first version does carry more of a tone of "stop and imagine what you would think" whereas the second assumes they've already thought of it. The second does sound a bit weird written though because the first part seems to be past-tense, then it switches to questioning what it might be like.

The questions have the same meaning. The wording of the two questions are just different. :)