in my opinion you are better off getting a good second hand machine for e.g. a Bernina 807 or an Elna SU air electronic, both sturdy machines used by schools and can run over layers of denim without fuss. I sew a great deal and worked for many sewing...
easiest way to find out... take it to a sewing machine repair shop - they can clean and tune-up your machine (you should do this about every year or so) and they will GLADLY show you how to thread the machine, change needles, etc.. (or you can try to...
The prewound bobbins you describe are specifically used for machine embroidery and not for regular sewing or quilting. You are better off buying a quality brand of thread (e.g. Gutterman or Mettler) and winding your own if you don't want to buy the s...