I"m getting married in July at a lodge and for my decorations I'm using blue mason jars with a mixed flower bouquet in them, colored stones in the bottom and a ribbon (whatever the colors of the wedding are or just some twine to give it the country feel) around the top part of the jar. They look really pretty, and are inexpensive to do as you can get fresh flowers from a greenhouse this time of the year or even Walmart sells mixed bouquets for about 10 dollars that look pretty nice, and can easily be split up or arranged with some greenery however you'd like.
Also I'm going to use the mason jar again with stone in the bottom and then a candle inside of it to light a pathway for our reception. For some additional lighting I'm using Christmas lights that can be wrapped around poles, sounds tacky but it looks really neat, especially with the barn wedding your trying to decorate, straw or hay bales in the corners or outside for some extra seating.
I don't really have any advice for the flooring other than when the dirt is packed it's as hard as cement but a white dress will still get dirt on the bottom. If there really going for a country wedding, you could use pine shavings on the floor, there pretty cheap and can be picked up at any country supply store. Good luck and don't stress. ... View related article.