We won't know if your sump is big enough cause u never stated the size of your main tank.
Generally I would recommend ulva compared to caulerpa..caulerpa have tendencies to turn sexual and die off.
You can't use a canister to draw water into your sump...considering you will be activating 1 more pump to pump the water back up..you will end up with water overflow either in ur main tank or you sump. Just get a hole drilled in new tank or your existing 1..or get an I-box.
LS = lifestock? Of cause lifestock is needed..