[cre]

Yes, you'll need to add resistors to the turn signal circuit to maintain a normal duty cycle... or convert to a digital flasher control instead of the stock flasher relay.

The tail lamp failure module will complain. You have three options here: Add a resistor and hope you can get the load just right to please it; Take the module apart and retune it for the much smaller load values (I've posted info on this here or on SM); Delete the module altogether.

You may fine the LEDs are dimmer. Omni directional LED clusters don't reall project a whole lot of light in any one given direction and they don't point it all where you want it. My suggestion fore the best possible visibility and best looking lighting is to buy some of the rectangular LED lights used in commercial vehicles (delivery trucks, semi's, ambulances). They come large enough to fill up each section of the MKIII's tail lamp housing, are very bright, really are DOT approved and some even come with a pulse circuit. Just remove the housing they come in and put the circuit in your housing... secure with hot glue or whatever and wire it up.