I can definitely help you out with sounds. I have a ton of steam locomotive sounds if you want me to share them, as for animation work id study animations and videos of the locomotives you're trying to model and possibly start off with something smaller like a switcher. Also for all your engines it might not hurt to find a way to state the minimum curve requirement in the store page, different locomotives need wider or tighter curves. And it would help people with designing their track layouts. Another engine i can think of that id absolutely love to see is N&W #611. #611 is my favorite steam locomotive and id be over the moon to have it in Farm sim. If you're looking for models I'd recommend turning to content made for Trainz. I've played games in that series for a long time and I've come to find tons of nice models.