Loving this conversion. I'm slowly doing somethign very similar. I own a pininfarina folding bike, which is pretty much a re-badged Dahon Espression.
The only modifications i've done so far are Saddle / Pedals (Shimano Combination spd) / Ergon 2 Grips on handle bar (temp solution until I change to drop handbars).

My intentions are to convert to drop handles, but potentially retain the 26" wheels using slicks, along with the stock brakes.

My question: If I kept my entire groupset as is and simply added drop handbars and Shimano Tourney A073 7 Speed Triple STI Lever Shimano Tourney A073 7 Speed Triple STI Lever Set | Evans Cycles

Would these be compatible with the current 7 speed cassette / RD / FD of the stock Dahon espresso?... would it be a simple transfer across?..

Thanks
Dan