For the night photos do not select a glossy finish, the glossy finish generally makes it more difficult to see the stars and makes any noise or grain the photos stand out a lot more.
For non-night/star photos any of the finishes should be fine, but if you are hanging the photos in an area with a lot of windows or light sources I probably wouldn't select a high gloss finish since the gloss will reflect the light and make it hard to see the picture.
When you add the picture to your cart make sure you select None for the crop option. You can select any size print and then select None for crop in your shopping cart and it'll print the entire photo instead of just the portion it shows prior to your shopping cart. When you select none it adds white bars to the photo to fill in any space.