The requirements of an "arsenal" for my mind depend on the kind of conditions you're going to see, in combination with how versatile you are as a bowler. Then  you have to take into account how many balls you want to carry around/how much money you have.

I personally look at reaction characteristics and look for early and late reactions for the three major oil volumes, light, medium, heavy. This gives me options on differing lengths also. I generally go for mildish drillings, I think the closest ball I've got to leverage is 2" then 4.5 nothing between those boundaries, as the reaction becomes unpredictable for me.
From what I've heard from a friend of mine who's with Storm, the T-road solid is an excellent ball, very versatile can be used from med-heavy to med-light with the right layout and surface. I think this would be a good ball to use as a benchmark ball as it should give you a nice read of the lanes.
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Reporting from England