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I think that's kind of a cool idea, the dinosaur park. Except that it's going to take quite some effort to get proper graphics (read: animations) for dinosaurs, even for top-down. But then again, it's all about searching for that one affordable artist who can pull it off.
It does sound like that you don't know where to go with your game. When starting, I personally find it best to have a good idea of what the game should be. Admittedly, I start with an idea, visualize it on paper, and then 'wing it' as I go by adding more features and ideas. Anyway I digress.
Just saying, perhaps it would be easier to give your game direction if you had an idea on the table. All it takes from there on are audio, graphics and programming. I think you are at least capable of the latter.
If you want the game greenlit on Steam then I think it will need to be in an advanced stage. Like where you have a small demo, but the graphics and perhaps audio, or at least a soundtrack in place. People can be crude, especially with the flood of new games in that section.
So if I were you, I'd really think well about platform and the idea. If it would be a theme park in RCT style, then people on Steam might be like; 'what is the added value/difference with Planet Coaster, Parkitect etc.? But if you go to the Kongregate or Newgrounds then you'll have an audience that love to play these small 'in a box' games.
Or at least that's how I view it.
Also, you could collaborate with an artist. I don't know how much exactly, but art may cost you hundreds of bucks.