Answer to question #1 I’d recommend PartsTree if you don’t have a good repair shop in your area. Reason I recommend going to a repair shop first, is that they can double check your part numbers and if they make a mistake it is easy to return.
Answer to questions #2, I doubt if anyone will be able to do so. We are not standing next to you with a strong drink in hand to see what you see. If you are replacing the piston, then do the rings also. Here’s the questions we have for you.
1. How experienced of a mechanic are you. This will dictate what we recommend doing?
2. How much money are you willing to spend? Subaru parts can get very expensive.
3. How deep into this rebuild are you going to go? Replacing piston and rings, deglazing or honing cylinder, cutting and relapsing valves, rebuilding carb. All these areas will dictate our answers.
4. Do you have the tools and equipment to do the job you want to do. Or a good repair shop to assist you?
If you post back, make sure you include all engine numbers and a few pictures of what you see inside. Here is a service manual which might be of some help. Remember that there are many good techs here to help, but we are hundreds if not thousands of miles from you so you must help us.