If that thing kicks over, it'll probably start with just a carb cleaning. It's also pretty hard to fuck up a carb cleaning. The hoses can dry up and become brittle, so be careful removing them. They only really go back one way, but take note of what goes where. It will probably be fine without the air ox, but check the plug frequently for a while after getting it going.
I would only replace one thing at a time, so maybe just replace the missing pipe for now. Treats has plenty of pipes for these bikes. $200 seems like a decent price, especially considering the whole bike was $150.
The battery is likely dead, you can order a replacement from Amazon for like $20.