Hi! I started by using my own website but the last few months I went for Picasa. In Google+ you can find a lot of photographers and registering there gives a great amount of Picasa space - it's nice to read the comments, see what pictures are viewed the most and linking is easy. And if you link the picture, you can choose from different sizes instead of uploading the same picture in various resolutions. But the upper limit is 2048 pixels.
The D5100 is a good camera - I wish you a lot of fun with it.