My advice to you should you win the lottery

is to give me half and I will tell you how to go about it.
On a serious note, the first thing you need to do is find a Class III dealer who knows what they are doing. This is one purchase where you do not want the process screwed up. The second thing is to call your county sheriff to see if they would sign off on it (some make it impossible). The recommended way to avoid the local LEO sign off is to set up a trust. Once that's done, have the dealer help with all the paper work, buy your auto sear or FA rifle, send in paperwork, pay for stamp, and wait an eternity
There is a lot more to it but that's the abbreviated version. Your dealer (if they're good) will walk you through the whole process.