my suggestion if you race 1/8 e-buggy (I did for the last 3 years)
in 4s:
esc hobbywing xerun 120a sct (smaller, smoother, lighter, cheaper compared to the 150a which is NOT needed, plus the 120a is sensored)
motor tekin t8 1900kv or reedy 1800kv
lipos SMC is definitely a good choice, for cheaper you can get nanotechs and zippy compacts are good too (no need to go hardcase)
servo (you get what you pay for on these) I would say futaba brushless or ace ds1015, savox are cheap but in the long run...no and they often need an externa bec to work properly
radio/receiver sanwa 1st pick, kopropo or futaba 2nd pick, spektrum feels cheap and inaccurate compared to these 3
in 6s (higher voltage meaning a more efficient system and less heat)
rx8 gen2 esc
1400 tekin t8 motor
the eco is an excellent car, lots of steering compared to the 6, some had a tad too much play in the elements considering it's factory built so make sure to check the tightenings before you go on the track
have fun!