to get the upgrades easier you can glitch it, some monsters get stucked sometimes, so you just have to leave it there stucked, wait for the time, go do something else, and then comeback and you have all the upgrades ready.
the bonus on Skater Bonus 2 is jumping to the left like falling from the platform, but then moving fast to right and Jump again, you should reach the Bonus.
i bought the 4th member on Day 65. There is much more than luck, you gotta know how to spend your money and points.
Besides, Rogues help you get more money.