So I am thinking of setting up builds as you reach the arena. my assumption is that in beta and release leveling will be slower as there will be a lot more content to clear and story to explore. That should, in my head, also mean you would run across many more runes before reaching the arena. Assuming you have good luck with this you should be able to get one or two items at least with the perfect stats you want (not exactly t5 because of the risk of shattering but at least t2 of the top 3 stats to set you up for the arena).
I am assuming you would find only one epic item (4 stat rolls) that have 2 or more of the stats you want / need with a hashed mix of other items, some with stats you need, others that are just nice (like increased move speed) and a decent amount of throwaway stats on gear.
I am thinking the best set up for the arena would be to “farm” white and common items (1 stat roll) that have stats you need and to manually put the other stats on yourself instead of farming for hours to hopefully get a good rare or epic item with 3 or 4 stats you need. Again this is just to get a good base ready for whatever build you are planning to challenge the arena with.
TL;DR: I think the best plan for challenging the arena initially is to gather a lot of white and common (1 natural stat roll) items that have stats you need for your build and to manually enchant the rest on.
sorry if that was confusing to follow, kind of just wrote as I thought of it.