GuitarPro,
You have been given some very good advice by the previous two posters. I was, also, forewarned about same. But I, also, felt very strongly about the capabilities for laying out my song ideas in their fullness. Unlike yourself, I had no one to help round out the rhythm section of a band. It was me, myself and I

. So I sprung for a Fostex X15 4-track Cassette Multitracker, some years ago, which enabled me to do just as I had desired to. Studio quality? No way. But it was nice to be able to lay down multiple tracks and hear what the song would sound like if it
had been played by a band. I now have a software sequencer (Sonar 4PE), and
a Yamaha Motif ES7 - which also has excellent sequencing capabilities. But there is a real
serious learning curve to the both of them. I just recently acquired Sonar, and with my ES7 I am just beyond the tip of the iceberg with its operations (even after 1.5 years of ownership). I also have the Yamaha AW16g which (if you don't know) is a 16 track digital multitracker. I
love this machine, and would
only part with it for getting the upgraded model which, very recently, came out. I don't think that I would go the 'software' route if I were you. Instead, I would consider a machine such as the AW16g, which could be gotten for a really good price being that it's been discontinued due to the newer model. I found it to be a lot easier to conquer, than its computer-based counterparts, and this baby
will give you professional sounding results.
Give it a look-see. It just may be the ticket for you & your band.