I started with an express as I didn't have much $$ when I bought. It came with an 18" tube and extended mag (7 rounds).
As of now, the following has been done:
Specter sling
Tacstar sidesaddle
Speedfeed foregrip and Knoxx specops stock
wilson combat mag spring and follower
Soon, I will be changing out the locking safety for a rem non locking. Also on the list (potentially) is changing out the trigger assembly, but my Glock 19s entire frame is made of plastic, and it wears hard, so I am not worried.
A couple more internal springs and it will basically be a police model. I have put about 1000 rounds through and it is pretty smooth. No hitches either.
I am up in the air about putting ghost rings on it as I might be getting the fed tag and switching to a 14" rod. No sense in dropping the bucks on the sights if they won't be around for long. The bead with white nail polish does fine at buckshot range.