I've had great luck with certain fruits and veggies in wine barrels. Things that do really well for me: Garlic, leafy greens (lettuce, spinach), blue berries (they like acid, and it's much easier to keep acid soil in a barrel in CA, where we have alkaline soil naturally), peas, raspberries, herbs and tomatoes (especially the cherry types). The biggest drawback to them is they need more regular water than things in the ground do.
Things that haven't really worked for me: dwarf orange tree and dwarf peach tree. Makes little to no fruit. What they do make tastes bad (but I think that is a function of lack of cold/heat in NorCal + dwarf varieties usually kind of stink in the flavor department).
OMG, yes, put the blackberry in a barrel far away from the ground. Those things get invasive, fast (at least the kind around me, there may be less invasive varieties I guess). It's great that I can go out to untended lots and harvest all the blackberries I want, but I certainly wouldn't want that thorny mess in my yard.
I'm sure it's possible. I've never grown blackberries since they've always been freely available in the "wild" here I think you'll be fine on the pavers; I was mostly joking. If it were mine, I'd just keep an eye out for anything trying to escape, like shoots leaning over onto dirt from the top (also wouldn't put it past a blackberry to grow some legs and go looking for ground!!).
Don't be too disappointed if you don't get fruit the first year. Both my raspberry and blueberry didn't fruit the first year and didn't really go into big production until the third season. I'm in the third now with the blueberry, and it's covered with flowers and fruit. My raspberry makes enough that we get a handful or two of berries once or twice a week during its season. Not enough to be making pies, but enough to have a few with breakfast occasionally.