In future write down the component name instead of just a link, it gets annoying have to open 10 tabs to see the build.
1. Yes its compatible, though you dont have a PSU.
2. I would say its not, unless your an audiophile and have a significant sound system to hook it up too. If your just using normal stereo speakers or cheap-ish headphones, then a sound card isnt necessary.
3. Is this just a gaming rig? because if it is there's a few ways to cut down on costs without sacrificing performance. Also some small optimizations I can think of, but will depend if you intend to overclock or not.