I am also new to longarming and wonder the same thing about bobbins. I just wind two before starting a quilt. I figure if I don't use both, the odds are very good I will use most of the first one and maybe even start on the second one. I am looking at getting one of those nice bobbin winders that places sell, but even with that you would still have to unthread the machine if you only have one cone of the thread you are using.
I am looking on a website for some goodies for my longarm machine - $200 of stuff is already on my goodie list - better get busy and make some money with this thing so I can afford more toys ... lol
I just spent time at my local quilt shop getting tension questions answered - my bobbin tension was way too tight and once we fixed that I got better stitches. Now ... to unsew all the meandering I have done on a small quilt so I can reload it onto the machine and stitch it again - without the birds nests on the back! Live and learn ... Steve said I should buy a Towa Bobbin Case Tension Guide - goodbye to $75!
Looking forward to getting better at this - practice, practice, practice.