The PE770 is one of the least picky about threads IMO, but it does use 90wt bobbin thread normally. You could always adjust the bobbin case to use a thicker bobbin thread if needed. My BFF has the Designio 820 which is the same machine in a different color and she uses Madeira Burmilion 60wt bobbin thread in her machine without having to make any adjustments.
As for using it to quilt in the hoop, even with a 5x7 hoop you're limited to small quilting designs. Fine for a small wall hanging or a baby quilt but you'll be re hooping a million times for a big quilt. If I were going to quilt in the hoop I'd want something like the Janome MC500e that has the 8x11 hoop made for quilting.
Cari