I cant tell what truck you bought. Either way I would tell any one with any truck the same thing.
If you want the fastest upgrades buy a Brushless system with esc and a lipo battery.
If you want to stay brushed, buy a good ESC a good motor and a Lipo battery.
Its kind of simple.
If your looking to do one thing now and another thing later. Upgrade the ESC first, because with out it you cant run a motor much faster than what your truck came with. (Assuming its a RTR)
Original RC 10T, T4, RC8Te, Tekin RX8. Losi Ten SCTE, Slash 4x4.