yeaj, for a road-to-hybrid conversion, I'd as soon use a decent vintage steel frame,preferably one that was more of a touring bike, and less of a criterium bike (longer wheel base makes for a cushier ride)

but the frame geometry of a road bike is designed around you being bent over... for a flat bar bike with a more upright riding position, the tube lengths and fork angle/rake are likely all wrong.

when I built up my hybrid, I went through a dozen different stem lengths and angles before i found the right place for the flat bars, and then I kept trimming a half inch off each end of the flat bars til I got the bar width where I wanted (they are about 530mm wide). I'm using Ergon GP3 grips so I can alternately ride with my wrists rotated.

Flat bar shifters and brake levers aren't very compatible with the stuff on road bikes either, My hybrid started with an alum hybrid frame, so it has mountain style gearing, and v-brakes, which are much easier to find flatbar controls for. I'm using a 3x8 drive, rather than a compact 2x10 or 2x11, I settled on a 48-38-28 crankset, with a 13-26 8 speed cassette (I think its "V"?) that gave me just the right range of gears for the speeds I can sustain. you'll probably find that in a more upright riding position, the taller gears on a high end road bike just don't cut it due to wind resistance. I'm running some high TPI Vittoria randoneur tire they don't make anymore, 700x32, very low rolling resistance, and a nice cushy ride, and I can get by ok on gravel and hard pack dirt, too.