HI, Welcome to the adventure! It will take some practice, so don't be too hard on yourself. As far as cutting wide fabric, the only way I know is to tear it. If you buy yardage, get extra, because of the way it's on the bolt, it's almost always cut crooked & you will loose some getting it straight.
On your practice pieces, you can just put another piece of fabric on top of your previously quilted sandwich. Use different color bobbin thread so you can easily determine how your tension is coming. You can cut rectangles from your practice pieces, bind them & donate them to animal shelters, use them as washable floor mats or car or picnic quilts.