i think for the number of bottles of wine that you need really depends on the relatives, friends and friends of parents that you invite...
say if the relatives are heavy drinkers, and if couple has a big group of drinkers... then gotta cater more wine and liquor even if you only have 20 tables.. it really depends on the guests who are coming..
but yup usually if not sure, 1-2 bottles per table SHOULD be a gd guage la.. we're also not sure abt the majority of the guests, just go for the average, then if not enough, get from hotel then lor