1. Having an unrelated title available on AMazon won't meaningfully help your primary title.
2. Yes, you need an agent, but you need a new book to offer an agent. Agents make their money by selling manuscripts to publishers; they can't do much with books that already have a home.
3. Self-publishing that title should be easy enough (at least in terms of getting the product out there.) I suggest you use http://bbebooksthailand.com/ for both the print and the digital formatting. You can do the latter yourself for free quite easily, but I suspect you might prefer to pay a little to have a pro do it. It's not expensive.
And yes, again, you probably want to get stuck into both our getting published & self-publishing courses. YOu'll learn a lot and save a lot of time in terms of making the right choices. Good luck!