You need to check whether the venue you have chosen needs a liquor license or not. Most village halls don't or sometimes the locals just turn a blind eye. And in may places, if you bring your owm, no license is required at all.
For toasts, buy whatever you can afford. Champagne is the usual choice as it's a special occasion, but it's pricey so alternatives are things like Cava (the Spanish equivalent but they can't call it champagne!) or sparkling wine from any country. I personally don't like sweet sparkling wine but things like sweet Asti Spumante from Italy are popular and very cheap compared to even Cava.
I would advise buying a few different bottles to test them before buying in bulk. Another thing to consider is that not everyone likes bubbly - at our wedding we offered malt whiskey (my husband's favorite as he hates bubbly) as an alternative!
It went down especially well with people we assumed would be champagne drinkers!