He was there for three days before the shooting, so he had time to bring ammo one can at a time. As for the guns, I imagine he had them either broken into upper and lower so the length was reasonable or just in a long, rectangular Pelican case. It’s Vegas - not many questions.
I’m not sure why so many guns. I can see two or even three in case of jams, but beyond that it seems unnecessary. That may have been more about the fantasy than about the actual outcome.
“I imagine he had them either broken into upper and lower”
Yep. Probably in regular old luggage.