I've been in your shoes. I was my brother's best man, and being a writer, have helped my friends craft similar speeches. It's the kind of thing you want to get just right.
I'm confident I can help—on top of the wedding stuff, I've done a lot of ghostwriting, presentations, etc. I've got a good feel for timing and for striking the right emotional balance. You want to be funny, but also touching and sincere.
That last part is key. As you suggest, I'd need to start by talking with you about your relationships with the groom and bride, getting a feel for your personality. We need to be authentic, no? A few questions off the top of my head:
How did you first meet the groom? What was your first impression of him?
What kind of girl do you think he needs? How does the bride fill the bill?
Where do you expect to see them in 20 years?
What's the best relationship advice you ever heard?
If you could change one thing about the groom, what would it be?
What's one thing the bride doesn't know about him?
Anyway, that sort of thing. I'd love to help out, so let's see what we can make happen.