Don't trust the PA for monitoring.

The B1 is a very useful piece for the money.

For MIDI, you would likely find any of the Cakewalk/Sonar varants easy to use.

If you have MIDI ports on your soundcard, you won't need a USB MIDI interface.

MIDI is not sound; MIDI is code for froducing sound from a sampler or synthesizer. Think of it like sheet music. It tells the device it's connected to what pitch to play and when, how loud to play it, how long to hold it, etc., etc.

Don't buy a D*ll! This forum will give you plenty answers about sensible buys for audio PCs.

Once you pick a piece of software, buy a book on basic audio recording for that software, and use that to learn about MIDI, audio, balanced lines, and the basics of recording. They all start with the basics no matter how complex they say they are going to be.

Recommendations would come from the search function here. I would suggest a decent set of powered computer speakers with an active controller/subwoofer such as harman/kardons which will be cheap if you buy them with the system, they wont give you a flat frequency response but they will get you started.

Alternatively buy a set of active speakers such as the Yamaha MSP5s, which are so well respected on this board that I can't really recommend anything else close to the price.

Then once the bug takes hold, you can start filling out your pieces. Next major upgrade I do I plan to start from the end of the chain and work back, i.e. speakers, then D-A, then software and DSP cards, then A-D, then outboard, then pres, then mics.

Thats why suggest the computer speakers. Dependent on how your money runs you may very quickly decide you want to upgrade your monitors.

Add each piece and take time to get to know it. Read everything on this forum starting with the budget forum. Above all, enjoy, and welcome to RO!