I think we will discover that Paddock made enough money in real estate to fund his gambling habit...and the comps from that allowed him to impress his family with luxury hotel suites and limo rides. And I think the triggering event for him was a realization that he couldn't afford his new girlfriend. As an accountant, he did the math and figured out that sending her on cruises to impress her (remember he met her in a high stakes room) would drain his account in 'x' number of years. Rather than be humiliated, he decided to go out while he still had money. Throw in some daddy issues with a father who once shot it out with police in Vegas and the location makes sense.
Oh, and he was (in his mind) able to demonstrate that he was smarter than the rest of us, with his detailed plan.
Boring. No weapons deals, money laundering etc. Just an a##hole who tried to go out big.