points to post #9
To the best of my knowledge, the answer to all of those questions is, unfortunately, No. You can do clever things with forcefields and black background sprites to emulate #2, but #1 and #3 just can't be done as far as I know. Sorry.
Here, in the lower left of the Kelp Forest. There's a cave full of colored fish that follow you when you sing, and smaller caves branching off that have song symbols in them.
I don't think that fish form is ever required to win the game though, so if you'd rather not trek back to the Forest you should be able to win the game anyway. There are several treasures that require it, though.
Check your automap (Q or double click the minimap) for places you haven't been, and if there aren't any, try messing with things that you've seen and look interesting. If you are where I think you are, you're looking to get two pearls back to two stone heads by two doors, and then charge them to open the doors.
The big blue pod is in your Home Cave, right next to where it gets too dark to see? It's another one of those things that you'll figure out later. Aquaria has a lot of things like that. In general, if you find something, try everything you can do to it, and if nothing happens you probably need something else before you can use it. Just keep exploring, you'll get everything before too long.
Also welcome to the boards! Feel free to ask any more questions that you have and we'll try to give you a hand.