Base guitar all day long. And IMHO first song from the Theater is easier than third from the Concert Hall to cover. More mashing but less jumping between buttons in quick succession.
Done in 90 days. Buy rockets and wheels ASAP. Groupies helps you with style, BUT they die after a crash. Invest in tricks, as it will be the main source of points - every different trick counts as x1 multiplier - 5 different tricks = x5 multiplier. Also, after buying Baseball bat, buy Pole Vault, and use it after loosing height with the simplest trick, to get x3 multiplier and lots of points in no time. Hope this helps.
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