Literally just bought this Wednesday,
http://www.amazon.com/gp/product/B0089NVTDM/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1
It works flawlessly. You just have to make sure to configure for both in Dolphin
If you're going to be playing Smash Project M may I suggest a pair of Mayflash GameCube to USB converters. I used to use a 360 on pc and I sucked at tourneys trying to adjust to the GameCube controller. Then I got the converter and my tourney skills improved. You may need to get the controllers as well, but on the bright side you can use them for Nintendo games.
Instead of this "Raphnet" whatever brand for $35 check out the Mayflash PC051 that is currently on sale for $11.99. I use a Mayflash product myself. Works great!
Quick thing, you might have trouble with the L and R buttons, because the triggers have two functiosn, one analog and one digital. Analog being the hold lower function, while digital the actual button press, you may (or may not) have to mess around with Dolphins settings to get it to work as it would on a Wii. Other than that should be seamless.
Your laptop ought to handle it find. I run Dolphin on an i5 from a few years ago and a Geforce GTX 540m. Yours ought to be fine.
For the controller, have you seen this? It was one of the more promising adapters I saw.
I'm sorry but I don't think you will be able to play with more than one GC controller at once. The adapter only has one slot for GC, PS, XBOX each.
The best adapter for GC for use in dolphin are the raphnet and the 2 in 1 mayflash. The Raphnet is apparently better but I have the 2 in 1 and it works fine for two controllers at once, so it is up to you.
I do know that when I tried to use Mayflash's drivers it was shit. For my 2 in 1, I didn't even need them and the functionality was better without the drivers (For more info see my post here).
So, your adapter will work for a single GC controller, but it isn't the best adapter available. Also, try to see if it works without the driver first. Make the Mayflash drivers your last resort so to speak. Hope this helps.
Pretty sure most people use this one: