The Threat is Real, very real.

[NugginFutz]

...
One would ask, in a place like a casino based hotel where security is undoubtedly a very high priority, how did he manage to get all that hardware into that room without raising a lot of flags?

Easily - within common luggage. Lest you forget, an AR can be separated into two much shorter components with ease.

And, he had to make a lot of trips in/out of the hotel.

The killer had been staying there since the previous Thursday. He could have brought 2-3 weapons in each suitcase, completing the task in just a few trips. Spread this out over the course of a day or two and nobody would have raised an eyebrow. "Hey, all I saw was a guy with a couple of suitcases."

Were there no cameras in the hallways that might have seen him installing those cameras - and no one saw it? How can this be?

He placed a camera on a food cart in the hallway. All he needed to do was order room service, tell the staff to leave the cart, install his surveillance equipment, and place the cart outside his room just prior to the attack. As far as hotel security may have been concerned, some guy was hungry.