I used to change my blade every time I started a new quilt . . .but since getting my die cutter, don't use my rotary cutters nearly as often, so will have to work out a system.
As for needles . . .i buy them by the 100 for my sewing machines, sergers and quilting machine. For my larger Bernina which uses M class bobbins, I switch out needles with each new bobbin. For my smaller class machine, every other bobbin. On my quilting machine, before starting every quilt.