Couples, particularly 2nd time round, are sometimes eager to make sure that they select smaller, select gatherings of close buddies and family, with a better stress on quality instead of quantity. Many venues now offer the entire service and it is well worth taking a look at your fave hostels to work out if they have a license to perform marriage rites. Also remember the flowers you selected should complement whatever theme you follow.
So, for example, if you're going for simplicity, stick to easy flowers that are classic and understated. Some venues will have limited space and may want to re-use the area really quickly, so won't be able to deal with large quantities of flowers.