If you're having trouble getting your arms back farther, try holding the broomstick with a wider grip. The wider your grip, the farther back around you should be able to get.
"Squeeze your glutes" definitely means to tighten your butt. If you're getting a lot of tightness in your hamstrings doing supine bridges, try laying with your legs on the ground and squeezing your glutes first, then move on to supine bridges.
As far as breathing out on squats, don't do it until you get to the top. The abdominal tension that holding your breath creates helps with the lift. Read
this from StrongLifts.
Exhaling slowloy at the top of a crunch while keeping your abs tight is harder than holding the same position while holding your breath. It's a simple variation on regular crunches, but I'd focus on building strength through the main compound lifts first. The Squat, Deadlift, and OH Press will build useful abdominal strength.
If you get to the end of a workout and really want to do some ab exercises, try
L-Pull Ups, or hanging
L-sits, or
Hanging Knee Raises.