Well, Joe Biden says all we need is a 12 gauge, and I think everyone should have a double barrel 12. Nothing is more "classic" than that. Either longer barrels for field use, or coach gun length (either with, or without exposed hammers) there is nothing like a double 12.
I have that covered, with my grandfather's Ithaca flues Model, which has been in my family for 104 years! Except for the finish its the same gun as it was when it left the factory, custom ordered by my grandfather, 26", choked FULL/FULL, and with the stock to his measurements.
I also have a Chinese made coach gun (hammers), for fun. ITs also my home "ready" shotgun. If that gun winds up spending months in an evidence locker before I get it back, its not a great hardship.
#2 A good pump. 12 ga., preferred. I have Win Model 12s, and a Rem 870 Express (bought so I could shoot steel, if needed).
#3 what ever floats your boat. I think a .410 is great, light pest gun, beginners shotgun (for the light recoil) and expert's field gun (for the difficulty of hitting)
I have a bolt action .410 that was given to me by a friend, and a T/C contender with a .45Colt/.410 barrel. Its a great rat wrecker.
One thing I don't understand, why some list both the model 12 and the model 97 as "must haves". Either will do a fine job, and the model 12 is the 97 without the (few) flaws it has. If you have ever had your thumb over the wrist of the stock when you racked a model 97, you know exactly what I mean!