Welcome to the community. And, yeah, I can say from experience to start small and work in incremental bits. My first project I had near alpha. Unfortunately, I started it while I was still learning PHP and realized there was no way I would ever want to maintain that beast. lol
So, I scrapped it. Then I found all my time divided between work, women, and my kids so I've been making slooooow progress ever since. lol Start with a paper prototype though. You'll be amazed how you can forget even the most basic things of game design.
I sat down had printed all my pieces that I needed to try playing a round of my new game idea and... had no idea what to do. Who took the first turn? What were the most basic options you could take on a turn? How did you determine ranged vs melee combat? And on, and on, and on. lol Seriously, paper prototyping will help you catch so many things you probably glossed over trying to focus on the fun / cool elements of your game. lol
