yes, kimono can be worn all year round, though japanese people tend to only wear them for special occasions. It is popular for foreigners to try them in japan though, so you wont be seen as anything other than a tourist dressing up, its nothing strange.They type of material of the kimono worn changes with the seasons, so of course it will ba a thicker kimono than the yukata that is popluar in summer. You can also wear them with a Haori coat and scarf or shawl.
When choosing the kimono try to go with an in season pattern. You shouldnt have a problem finding a design that you like, in fact Autumn motifs are my favourite on Kimono, http://images.google.co.jp/images?hl=ja&lr=&um=1&q=%E3%82%82%E3%81%BF%...
May I ask what you intend to do in Kimono? is it just to try on? I would imagine it would be too troublesome trying to go shopping in kimono, but it would be lovely to visit a temple or teahouse in kimono, you would really look the part!