He had money to buy lots of guns. Let's estimate on the high end $2K per rifle? So $80K in guns and ammo? He wired $100,000 to the
ippines, so he had the cash covered. If you put a Do Not Disturb tag on your door knob, you won't be disturbed. When I visit hotels with our dog you bet your ass no one but my family better open that door. No reports of mauled maids so I can say our doors weren't opened. I think the shooting platform was just a chair or table from the room. If he made multiple trips with a guitar case, he would have blended right in. He was there for 4 days so he could have made quite a few trips. You don't need military training to shoot a slide fire into a crowd of 20,000 people. These weren't sniper shots, just spray and pray.
Not too hard to add it up but if you are looking for a sane reason to add up, you will never find it. The guy was a functioning psycho who kept the mask on well enough for no one to notice.