Fullish bat, with a small amount of concaving just to keep the weight manageable and arguably help with pick up, inch shorter blade for increased bat speed and a counter balance handle, mid-low middle given the likelihood of trying to smash Yorkers and therefore preferable no duckbill for added strength to the toe, I wouldn't want this made out of top end willow, there's no point in my eyes buying a bat you're going to use solely for t20 at the cost of grade 1+ willow, cheaper balls are normally used in club t20s and you're trying to hit everything it's likely it's gonna break at some point so would prefer something at a grade 3 price point.
I'd also want a decent bow, helps you clear the infield and again to me at least improves pick up