For me, using Pikmin Throw and changing the order with his whistle is by far the best way to utilize Olimar. My advice is to not throw Purple Pikmin, but rather use them for throws and Smash Attacks. White, Red, and Blue are best for the Pikmin Throw, and Yellow is really good for standard attacks and Aerials.
But that's just me XD Not many tips for Bowser, I'm afraid. Try using his infinite Claw Jump [It's in the AT Thread], and comboing with it.
As for Falco. Doing a dash grab works wonders for his chain throw. Use the down throw, though. So, Down throw, chain grab, repeat. Once you're done, and if your opponent doesn't fly far enough, use his reflector, because it usually always hits.