I don't think there are steps to achieve the pro status, except promoting maybe.
My Solihull Moors indeed received professional status when promoting to the League 2.
However, I discovered that it is wise to give all the players you use and your training staff a full time contract. It doesn't cost more and they'll train the double...
if your board feel they have the money then you could be pro in bss or bsn depends on the finances aswell as your postion but id think you would be pro if you got to league 2