#1 ... you can set your machine to the largest stitch size but if the quilt doesn't flow smoothly between the foot and feed dogs, your stitches will still be anwhere between teeeeeeny-tiny and holy-smoke-those-stitches-are-long! before you put it through the machine again, practice with a sandwhich of leftover denim, batting and backing. figure out how much help the sandwich needs to flow smoothly.
#2 ... you can tie it with regular thread. just use 3 or 4 strands together.
#3 ... ripping will not be much faster than picking (use the seam ripper to cut through the top stitch about every half inch or so and pull the top thread out. the bottom thread will come off on its own. you won't mess up the backing or batting that way.
#4 ... if you want to try quilting batting to one layer first, then quilting the remaining layer to the first two, quilt the batting and backing first. i'd recommend you do it with the batting on top or you'll end up with gobs of batting clogging your bobbin.
#5 ... either tie or pin before you go anywhere near the machine again. your quilt is too heavy to risk taking shortcuts. you'll just end up with the same problem you have now.
#6 ... if you have to stop every 5 minutes to scream into a pillow or kick a can around the yard then ... fine ... do that. but take your time with the quilt. pin, tie or baste with needle and thread from the center out. the spray is not going to be enough on something that heavy. to do anything else will just waste more time and end in more tears and frustration.
#7 ... i ain't makin' this stuff up. i am sharing lessons learned the hard way. use them to your benefit.