FWs are very sturdy machines but they will not sew if the needle is threaded backwards (they thread from right to left) or if the hook is not properly in the bobbin area. I would want the bobbin to be there as they are expensive to replace. It would be nice if there were extra bobbins because the ones you get at JoAnns or walmart don't always work. You can get them from Sewclassic.
One FW I purchased was very fussy about the bobbin case fitting in..... you need to make sure you hear the 'click'.
Good luck and finding the perfect FW for YOU!. And, if you need help, the vintage section always has people very happy to give advise..... good advise, by the way.