You should be fine as long as you use road flat bar controls instead of mountain flat bar controls. Shimano's road and mountain front derailleurs have different cable pull, hence two different kinds of flat bar controls.
If you get a good deal on mountain flat bar controls, my recommended set-up would be whatever 8-speed right shifter you can find and a cheap friction shifter for the front (Sunrace makes them, for instance). This nicely avoids all the problems associated with front indexing on a triple, and allows you to use whatever derailleur and crankset you want.