I definitely agree that you should start small, you could work on small projects to get more knowledge and experience and keep your dream project as a sideline and add to it when you are able, you'll be surprised how often little projects can bleed into larger ones, if you have your idea which in your case you do i would suggest getting a pen and a notepad and start working on a game design document mapping out everything you possibly can which you can always refer back to, once you have that finished analyse it and break every part of it into it's simplest form and that's where you can start your small projects from, never be afraid of trial and error, making mistakes and getting things wrong that is totally natural and actually sometimes some of the fun that goes into making games, you can't get tips on motivation that is something you will have to manage yourself but if you truly believe something is worth working on the sky will be the limit and speaking from personal experience if you can make decent progress save your work to a removable usb drive so you don't lose it if the worst comes to the worst as it did with me a good few years back when my pc broke down and i lost everything i was working on and i seriously considered never working on games again.
I hope you find this useful and good luck.