Sorry, forgot about Question 2.
A simple USB MIDI interface should be enough. As far as I know, most will come with both MIDI in and out.
Does your keyboard have a MIDI in as well as out? To play back the sounds on your keyboard it will have to have a MIDI in. Otherwise, you can record the...
You can download and try Reaper for free. It's super cheap to register and the trial version runs forever so you can be 100% certain before you purchase. There is a Reaper forum on this site (https://homerecording.com/bbs/user-forums-brand/dont-fear-reaper/) where you can ask questions.
It...
That's a pretty broad question. You should try recording something, playing around with it until it sounds good to you, and posting in the MP3 clinic for specific tips.
Audacity works fine on my PC. I also use Reaper, which has been great for me. You can try it for free, so you really have nothing to lose checking it out.