Pikmin and no you can't play it on the computer to my knowledge.
No. Those are two separate games. New Play Control! Pikmin is the first Pikmin with Wii controls.
New Play Control Pikmin is the same as the first Pikmin game; the same areas can be unlocked after traveling through each area.
No, there is no way to link the two games.
No. In Pikmin 2, you can play with up to two players only.
Both Pikmin and Pikmin 2 were originally released on the GameCube, though they were remade for the Wii (New Play Control! Pikmin 2 was never released in the United States). Pikmin 3 will be exclusively for the Wii.
No. Pikmin is not a game that features GameCube-to-Game-Boy connectivity.
Pikmin 3 has not been released yet, and thus there is no way to tell.
By pikmin you must mean Olimar, who uses pikmin. You already have him. He is one of the beginning characters that you start out with. There is no way of unlocking him, as you already have him.
The original Pikmin had no way of switching between colors of Pikmin on the fly. To switch colors, you need to disband your Pikmin with Y or C for Wii version and call the appropriate color to you. You can alternatively hold the throw button and press the whistle button.
You have to leave Pikmin idle by a Puffstool and call them at the exact moment they are hit by the Puffstool's spores. This requires perfect timing. Be careful, as Mushroom Pikmin will attack any other kinds of Pikmin.
Pikmin 2 is quite a popular but under-rated game. I recommend you play it if you haven't. It is incredibly fun.