I had a TT350 and made it street legal in a very easy state to do so. The first question I would ask is what are the min. requirements in your state?
f you want a kit call Trick Dual Sport for a version that will draw the minimum wattage. http://www.trickdualsport.com/
A kit would be similar to one for any XR.
You my be able to add a stator from an XT for more juice.
I would swap out the tail light with an LED 1157 bulb first.
The existing taillight has a third wire for a brake light that I would wire to the front brake using a hydraulic switch.
Swap the headlight for a DOT 55/60W low/high beam (if not using a kit).
If you do require blinkers get some LED versions.
TT350s are one of my favorite bikes of all time!