As for how big is too big... I would say 12 qts is a great size. (in terms of how big 12 qts really is, which I found hard to picture until I saw one, its 3 gallons, so you could picture 3 gallons of milk) It really isn't too big. I use it to make stock primarily right now because its just us two and its the only thing I "batch cook". (I make stock from 1-2 chicken carcasses, and could probably fit 3-4. I use it for cooking a lb of pasta, but could easily do much more. Basically, I don't find the stockpot too big to store or put on the stove, so I love it's size, but I've never filled it more than oh halfway (and that is making stock or a huge batch of soup to freeze), cooking for 2. (I don't batch cook too much). What I love about it's size is that this one stockpot works for me now as a couple, and will still work for me when we are a family of 3, 4, 5, or more, plus guests.
As for specific stock pot, I absolutely LOVE my all-clad. It has an aluminum or copper disk on the bottom, stainless steel, great handles (vital), a nice fitting lid, is not too tall or too wide (but far more tall than wide). My dad has a cuisinart stainless steel stock pot I think and I've used it a couple times. It's a good stock-pot. I don't think it is heavy bottomed, but that might not be a problem for a stockpot. I don't know how it will last, but it is a lot less money, and it does definitely appear to be a stockpot which will make stocks, soups, chili, large batches of tomato sauce, pasta and more for years to come.
The features I would look for are:
very well attached and strong handles that are big enough for your hands plus pot mitts to fit
a good fitting lid
a heavy bottom (this might be a disk of copper or aluminum or even stainless steel, or something else. it can look like many things. it even could have a layer of copper or aluminum throughout though that would be too heavy for a stockpot)
12 qts
taller than it is wide (this limits evaporation which is useful on stock, soups, stews, and pretty much everything you use a stockpot for). You don't want it to be too tall to look into though.
a good stockpot is such a useful tool