Which belt are you refering to as a serpintine belt? If you are talking about the AC and Alternator belts, they are easy to find and can be found at subaruparts.com if none of the parts houses don't have them locally.
Here is the link to the
instructions to replace the spark plugs. It is in the How-To Documents for future reference. Some of the other tasks that you mentioned are there too.
Good luck.