You can keep them outside year round. In the winter they need to have a barrier from strong winds and snow/ice, in the summer the males will go sterile if temps stay in the 90's for an extended period. I use heat lamps and tarps for my outside rabbits during the winter. In the summer I have fans blowing through the cage area. The ones housed inside a building are kept between 70-80 degrees.
On the rabbit poop, yes you can use it in flower beds as well as a garden. It is a "cold" fertilizer, which basically means it won't burn your plants or garden such as horse/cow and chicken manure that needs time to get the high amounts of nitrogen out.
You can also scoop the poop and put it in your empty feed sacks and sell them on craigslist or if you can find some local organic garden clubs they would also probably buy it from you for $5-15.00.
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