Ammo...as pointed out by stgb, they should do OK with most anything from a minimum of 1 1/8oz of shot and up.
Shotshells (not always with Buck or slugs however) will be marked in the following manner...3 1/4 / 1 1/4 / #8...or similar...the first number is the amount of powder, measured in "dram-equivalent" (3 1/4)...just remember the higher this number is, the more powder and, usually, the more velocity and recoil...second number is the weight of the shot charge in ounces (here it is 1 1/4oz)...and the last is the size of the shot (#8). This just happens to have been my most favorite dove and quail load years ago when I hunted...maybe one day I'll tell you about the dove I killed in Georgia while he was perched on a cloud!
The larger the shot size number, the smaller the shot...no, it does not make sense...we are speaking about shotshells, and many things about them defy logic.
There are some very light-loaded shotshells out there for small game hunting, clay target shooting and practice, etc. many with only 7/8oz. of shot. The Benelli needs a certain amount of recoil in order for the inertia operated action to function correctly, and typically, these shells do not provide that minimum level. While they won't harm the gun, they will probably be a PITA with failures to eject or feed the next round, etc. The major US ammo companies are also making "reduced recoil" or...good marketing move here..."Tactical" Buck and slug loads these days that are working very well in the field. You will probably find that after a few hundred rounds of lighter, less expensive loads to get it well broken-in, your Benelli will function with most, if not all, of them. Mine have zero problems with the Federal Tactical loads or slugs. I have never fired any Rem. or WW reduced loads in them, so cannot say for sure about that.
"Standard" Buck and slug loads are more powerful than the reduced / Tactical loads due to having more powder and, sometimes, more shot as well. The Benelli will thrive on them, but your shoulder may complain. The 2 3/4in. "Magnum" loads will contain even more powder and shot, and will...I assure you...definitely make an impression on you! You do not need any 3in. Magnum rounds for defense use, even if you should have a gun that will fire them. They will have more shot, but will deliver lower velocity than the "short magnum" loads, reduce magazine capacity, and generally are not worth the added expense or added recoil.
Manufacturers are constantly changing loads, playing with different powders, shot hardness, and stuff with ALL ammo...not just shotshells, and shotguns are the most "individual" of firearms in the respect that your gun may shoot great patterns with a specific load, but the very next one off the same assembly line will not shoot that load for shit...go figure...but it is the truth. YOU will need to try several different loads to see which your Benelli prefers. My preference runs strongly to Federal Tactical for reduced loaded Buck and WW for standard loaded Buck, but many here get excellent results from other ammo. I will not shoot most foreign Buck or slugs in my guns because I have seen too much of it that is pure crap, but some guys use various stuff that seems to work fine for them.
This is only very basic and minimal info on shotgun ammo...do some web searches and read up on it...there is a lot to learn, and I sure as Hell don't know it all!