If you want to get inside without having the alarm sound right away, step up to the bouncer so he notices you and then back away so he doesn't get alerted. After a few seconds he'll step aside and let you in.
There are numerous locked doors through the club, and they have numerous ways of getting them open. Doesn't matter how, but get all of these doors open, as there are safes you need to get into behind them.
One of the two safes will be filled with money, this is what we need for the mission. Bag up the cash and keep it safe until the van comes.
If you bought the Loot Truck asset (which is a smart investment), you can throw the bags into a truck that arrives way faster and in a very good spot.
The other safe that didn't have money will be filled with coke instead. The coke isn't needed to finish, but it's a nice way to get some more cash.
Eventually the van will arrive. Throw any bags you didn't throw into the Loot Truck into the van now, and escape.