We had planned to have our piggies outside (although that is currently under discussion, anyway...).
Get a well made, pre treated hutch that is suitable for outdoors.
Also investigate hutch covers. We choose a hutch that came with it's own thermal and waterproof cover for the cooler months or wet days.
Think carefully about where it will be positioned - close to the house, slightly protected, and not in full sun is good.
Bring everything home and get it all set up before you collect your guinea pigs, so when they arrive they won't be sitting in a carrier while you fiddle about with bedding and water bottles!
Give some thought to food storage. We got a couple of large plastic bins with locking lids for hay and bedding. This keeps everything dry and away from rats. We put a couple of bricks in the bottom of each bin to stop them blowing over when it is windy. Food is stored in the house, by the back door.
Look at your garden security and plan to protect the hutch from predators (cats, foxes, etc). We also have a continual stream of kids in and out of the garden, so bought extra bolts and locks for the hutch doors so they couldn't be opened by accident.
As for bedding we started with Auboise and so far are very happy with it. However although we bought a large sack (35 liters) we always knew if we didn't like it we could change at a later date.
I hope some of that is helpful. As I said at the start our pigs are still inside because they came home earlier than planned and it was simply too cold to put them out just yet, but we did a lot of research, and some of the above are things we have done with a view to them living outside.
