I think it sounds like a great plan (but I am surprised you choice Vegas instead of WDW!

)
I would do the same with the bar. DH and I are not drinkers, so I don't really see paying for other peoples. Besides in Vegas people can go a little more wild that way then maybe at home.

Buying one round for the toast seems fair, then they can decided if they what and if they want to drink after. Paying for the meal and tip is the right thing to do.
I don't think you should do anything official after. It isn't like there is nothing to do there. I am sure people will be fine finding their own activities.
I hope you have a wonderful wedding and I can't wait to see pictures! One year, that isn't long now!