Get the best power plant (helps to keep your ship cooler), power distribution (boost more often), thrusters (gives you better manoeuvrability and max/boost velocities, the latter is the most important in your case). If being interdicted - submit, i.e. idle the throttle and do not perform evasive manoeuvers. In this case your FSD won't fail during interdiction and the cool down is going to be very fast so you should be able to initiate SC much faster unless you get a mass lock. Equip your ship with chaff launchers so that if the enemies rely on turreted or gimballed weapons they will have trouble aiming at you. If you run without the shields then it is better to avoid combat at all costs. T6 and all other traders have weak armour and are very easily destroyed.
As of the error you received trying to buy the shield generator - it is not compatible with your ship. You need a larger shield generator. The minimal size of the shield generator for T6 is 3.