I'm thinking now it may be simpler to go with just the bar-end shifter and two cross levers on the flats. If that all works out, maybe I'll get more advanced and upgrade one of the cross levers to a TT lever+interrupt.

My main reason for wanting the TT lever was efficiency -- it seemed silly to let a bar-end go unfilled while I was putting something in the other. But I think for a first-time big conversion I should go for simplicity first.