First time buying parts ( derailleur, chain, rear axel, shifters) need help!
There a good chance that the combined cost of the parts you need will exceed the cost of the bike. The Next brand is a brand sold at discount retail stores. They retail for around $125. Many of the parts are not available as new replacements. The easy method is to say throw it away. There are some alternatives though. Many cities have programs called recycleabicycle.They teach youths how to repair  bikes in an "earn a bike" environment. If you don't qualify for the program they make accept the bike. The other option is to contact your local bike shop and see if they have some used parts available. If you check your local Craigs list or similar listing you may find another bike that is free or inexpensive enough that you can put the one bike together with the parts from both.