1. Last month John and I had our meeting with him to go over the details, and he said "the church (we attend and I am a member) does not charge for officiating weddings. However, if you want to give a gift, that is up to you."
I believe what he was referring to is a donation to the
church, not to him.
When I was researching my book, I ran into a lot of conflicting info about what to tip the officiant (apparently it can be considered an insult in some places but is practically expected in others!), but most sources say that if you are getting married in a church, you should make a donation to the church if they don't charge you a fee to get married there.
Personally, I don't really see why you need to make a donation to your church if you're not actually being married there. It's not like somebody has to open up and turn on the lights for you, and you probably already tithe. I think you've done plenty for your officiant. We paid for our officiant's flight and 2 nights of hotel, plus his meal at the rehearsal breakfast, and he came to the reception.
2. how much do you tip the limo driver? Since the limo is provided by WDW I am not sure of tip amount. Four hours - 3 trips to wedding location, then 3 trips to reception location.
As you surmised, the limo drivers are not Disney employees - they work for Mears. And even if they were Disney employees, they should still be tipped. There are only very few Disney positions that are not allowed to be tipped, and those people will tell you so if you try to tip them (Sales Consultants are about the only ones you'll come into contact with who can't be tipped).
You could figure out 15% or 20% of your bill to Disney for the limo, but I think most people just slip the limo driver a $20 or a $50 or whatever they can afford.
3. Can wedding attire be worn on the buses?
Yes. The only prohibition on wedding attire is inside the parks.
