Be aware that that Focusrite interface posted above doesn't contain any midi ports, which only matters if you needed to plug in any actual midi cables (like to some legacy external gear).
Most newer stuff connects through USB to the computer, so it will likely not be an issue - just trying to make sure you get all the info :)
That interface is a good one - great quality and reasonable cost, and it will really make a huge difference in the performance and in the sound quality.
That interface has 2 mic inputs, so if you pick up even a standard stage mic it will likely give you as good or better sound than the current USB mic you have been using. (I don't believe those USB mics have much oomph - from what I can recall when I have seen them in the past).
I TRULY hope you get it all worked out, and that you quickly get to where what's in your head and in your heart can be expressed through Sonar into stuff other folks can hear and appreciate. :)
This forum has a bunch of really helpful folks, and as long as you don't make too much fun of some of them driving on the wrong side of the street or typing with an accent, they will put a lot of work into helping you get stuff figured out.
Bob Bone