You can try for a Mesa Tactical shell carrier.
I personally recommend just getting something like this:
and use a high-strength OUT-DOOR rated double-sided tape to attach it.
Thats pretty much exactly what I did to add a shell carrier to my Benelli M4, and it works 100 times better than the method Mesa used, and it wont damage your receiver at all. Also it wont add too much extra weight.
If you want to go with a red-dot, go with something light, like an Aimpoint Micro, or a Docter/Jpoint type sight. Tactical Shotgunner also carriers picatinny rails for the Beneli M2, although you may have to thread and tap the receiver.
As for lights, there are TONS of different ways to attach them.
Something like a barrel/mag-tube clamp with a rail (such as Nordic-Defense) or the Mesa Tactical one, would work. A lot depends on where you want to put the flashlight.
(This is an old pic, I have taken the top of the FAB Defense railed forend off)
This way, when holding the shotgun normally, my thumb sits just behind the flashlight tail cap.