I recently picked up an 870 for $100 and am not sure what model shotgun it is. It looks like it could be the Model 870 Express Super Magnum Synthetic that is on Remingtons web site. The barrel says 12GA, 2 3/4, 3. 3 1/2 only with super mag. receiver but the receiver only says Remington 870. Is this the proper receiver?

I have never owned a shotgun and bought it for 3 gun matches so I will be doing a lot a shooting with this 870 but am kind of lost when it comes to chokes and types of barrels. I have some other questions about barrels.
1. Is there an advantage to having a ribbed barrel?
2. Is there a benefit to having a rifled barrel vs a smooth bore.
3. Is there any good sources for wood forarms, I can't seem to find any.
4. What type of choke if any should I use for 3 gun that will be ok with slugs?

I will be adding XS sights for the rear and a trigicon for the front and a MESA rail w/a six shell side saddle. Or a rear sight with integrated rail like something on the 870 express tactical and a side saddle separate.