My opinions differ from the rest of you guys...
For guitar amp, that is very important, without that, guitars really sound dull. Line in on guitars is worse than using a $10 mic. I feel you need to get a guitar amp as it's more practical. Than get a SM57 (many others can be used too) to mic the amp.
Get a USB mixer for your inputs, toneport ain't very worthy as it only has 2 inputs and cost pretty much. Get a USB mixer from Yamaha or M-audio, that will really solve your problems on inputing to the pc.
For bass, just get a DI box, they cost roughly $200.
The SM57 can be used for vocals, though not fantastic. You can start with that first if you are really tight. Ultimately, a good condenser would be worthy of choice, find one that fits your voice well....