>>152581465Do the quests that unlock items at the Pianta parlor (You get a special card, then a silver, etc.). You can buy power rush badges for around 60 piantas each I think (180 coins). You can use the slot machines for easy piantas, just watch for the roulette to flash orange (The 7) and time your presses to land on it.
You won't be able to reduce your hp to 5 until after chapter 5, which means you'll have to beat cortez with 10 hp, unless you actually upgrade your hp beforehand...
You may also want to find some pretty lucky (Found on spinia/spania) and close call (found on koopatrols I think) badges.