Different instruments hook in differently on the wii. Mics all fit in through a USB slot. The keyboard also only fits in through USB, but that's because the only version of it is the Rock Band version. The other instruments are all dependent on which kind you have. Guitar Hero drums and guitars are wiimote extension controllers, meaning you plus a wiimote into them rather than using a USB slot. Rock Band drums and guitars are USB slots (direct USB cable for Rock Band 1 Drums, wireless dongle for the others) So technically speaking, you could get away with 1 mic, 1 keyboard, and use 2 GH guitars and a set of GH drums, and you wouldn't need a hub, but you would'nt be able to do harmonies.
So, can I connect the drums dongle and the guitar dongle. Then connect the keyboard dongle to the guitar one and still have 3 free slots for the mics? (2 from the keyboard and 1 from the guitar dongle)