I'm running 3 b4's at the minute two are brushless and one brushed. Two for the boys and one for me. Nimhs are the safer option for little hands connecting and disconnecting batteries. 3000mah are fine, esc and motor wise I had a tamiya esc laying around and bought a motor from modelsport for a fiver, plenty fast enough to start with. You could get something quicker and trim the end points down on the transmitter, this is what I've done for my eldest son, can slow it down for the track and open it up for bashing
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