As an owner of a couple benellis (SS 12ga, Monte 20ga) a few Berettas (2 686 12ga, and an AL391) a Mossberg 535 12ga, Browning Super 20ga, Winchester ...... Well you get the point, I have a small opinion on the matter. 1st off, dump the idea of a 20 ga as an "all around" shotgun gauge; 12ga is your all around. You can load it heavy for turkey, deer and long fliers like phasant. You can underload it (not light much with the Inertia drive ) for smaller game like grouse and dove. It will give you a higher pellet count than in a 20ga (duh) and the means more chances to break/kill.
As for the length I think you are on the right track with the 28" for a "overall" choice. It is a litte long for the turkey woods but will work. I used a 28" Nova for years!
For the model, SBE2. Will cycle everything from light clay loads to heavy 3.5" turkey loads & slugs. You cannot beat this gun for the money! If I was only allowed one Benelli (heck, if I was allowed only one gun) it would be a camo SBE2. I do like the black better but for the duck blind, turkey blind, dove field etc sometimes its the little things that count.
NOW after all that. My favorite gun in the safe right now is my 30" 12ga Super Sport. I will go 98/100 on a regular basis on the skeet field and 97/100 on the trap range. It is GREAT for dove and pheasant. A little long for tight cover though (grouse/quail).