I'm not the best fantasy player out there, but I did run ogres for about a year.
You are off to a very good start on what models you need.
You gotta have the Tyrant - he is just such a beater. You also HAVE to have the bulls, you are required to in the army list.
From here I would look at Ironguts. They are just nuts - make em 3 wide and two deep and you will have 18 s6 attacks coming.
Other than that just play a few games and see what you like. I myself don't like the gnoblars, I would run trappers instead since they fill the requirements to field the scrap launcher.