Novice flyer looking for advice on canceled flight

My wife and son were traveling on American Airlines from BGR -> DCA -> IAH for a homeschool conference, and I’m trying to understand:

1. what happened operationally,
2. whether any compensation/refunds are realistic,
3. and what we should do differently in the future.

We don’t travel often, so this has been a learning experience.

Original itinerary (booked through Expedia about 2 days before departure):

• AA5061 — BGR -> DCA
• AA5639 — DCA -> IAH
• Original scheduled arrival into IAH was about 4:12 PM

The layover at DCA was only about 45 minutes, which in hindsight may already have been risky.

What happened:

• The first flight into DCA was delayed
• However, my wife and son still made it to the gate for AA5639 on time
• They were then removed from the flight because the aircraft was supposedly over a weight limit
• They were told that because their tickets had only been booked a couple days earlier, they were among the passengers removed
• American rebooked them onto AA5461 departing later that evening
• American also issued meal vouchers and future flight vouchers

There were also a couple things that confused me:

• We had paid for first class on the BGR -> DCA segment, but my wife ended up seated in main cabin
• AA5461 then experienced multiple rolling delays
• From what we could tell, the aircraft for AA5461 was arriving late from New York
• Around 9 PM they were notified that AA5461 was canceled and they were rebooked onto AA5074 departing after 6 AM the next morning
• American classified the cancellation as weather-related
• I'm not sure how to verify, but I think weather was fine between DCA and IAH so it seems like they could have still proceeded with the late flight

At that point:

• They needed sleep before attending the conference the next day, so we paid for a hotel near the airport
• We also had to rebook the rental car because it was too late to modify the original reservation, and the replacement booking cost more

American did provide meal vouchers and future flight vouchers, but we honestly don’t travel very often, so vouchers may not be especially useful to us. We’re trying to understand whether any cash refund/reimbursement options are realistic here.

My questions:

1. Does this sound like a normal weather/ATC cascading delay situation?
2. Is the earlier removal from AA5639 likely considered involuntary denied boarding, or do “weight restriction” removals work differently?
3. Are we entitled to reimbursement for the first-class downgrade on AA5061?
4. Is there any realistic chance of reimbursement for the hotel or increased rental car costs?
5. In general, what should inexperienced travelers do differently to protect themselves from this kind of domino-effect disruption?

Thanks in advance. I know experienced travelers probably see situations like this all the time, but this has been pretty overwhelming for us.