...serial number is M232xxx.
1) is this pre ban?
NO! I saw on the net somewhere that a guy had a M19833X and that was manufactured 9/19/94. I am pretty sure that yours is post ban. Call Benelli customer service and get the exact date for yourself.
2) the gun has no boxes or papers and the muzzle is unthreaded, no chokes. Is this normal? all the info I have found on the net and speaking to benelli is that the gun should have had a threaded muzzle and choke tubes.
I am not sure it is nromal, but some barrels were manufactured like that. You could always buy another barrel that has tubes, but obviously that adds to your cost. If you really want the shotgun then use this as a negotiation point to offer a lower price.