You seem to be confusing MIDI with Audio.
MIDI is only for control data. It is for messages such as note on/off, pitch bend, patch change, etc. No sound goes over MIDI. When you mention "good quality MIDI sounds and effects", what you are really looking for is a synthesizer with a good set of patches, that also supports MIDI.
With that out of the way, I recommend you buy two pieces of equipment:
- 88-key Weighted Keyboard
- USB or Firewire Audio Interface
You have many choices on both. I actually recommend you look at some of the "workstation" keyboards. These tend to have a very wide variety of patches, and are extremely cheap if you get an older model. My Roland Fantom was a beast when I bought it in 2001, and is still a beast today, but you can pick it up for ~$300 used, which is a lot cheaper than the $1900 it cost new. You'll see similar pricing on keyboards from Korg and Yamaha, if you are patient and look around.
As far as the audio interface, if you only want to plug a guitar in, then you don't need anything with a lot of channels. M-Audio's Fast Track fits your bill, and I've seen these in music stores for around $50.
For the whole Firewire vs USB argument, that has already been covered here: https://video.stackexchange.com/questions/41/firewire-or-usb